Why was the Old Testament so important to the writers of the New Testament, and why is it important to mankind today? Let's briefly summarize some of the things it reveals to us.
• It reveals God—that there is a Creator, that the world didn't just happen, and that He is in control over everything at all times (Genesis 1; Isaiah 46:9-10 Isaiah 46:9-10  Remember the former things of old: for I am God, and there is none else; I am God, and there is none like me,
 Declaring the end from the beginning, and from ancient times the things that are not yet done, saying, My counsel shall stand, and I will do all my pleasure:
American King James Version×).
• It reveals that this God is a God of love who is deeply concerned about every person who has ever lived, and that He wants to share everything with all of humanity (Psalms 8:4-8 Psalms 8:4-8  What is man, that you are mindful of him? and the son of man, that you visit him?
 For you have made him a little lower than the angels, and have crowned him with glory and honor.
 You made him to have dominion over the works of your hands; you have put all things under his feet:
 All sheep and oxen, yes, and the beasts of the field;
 The fowl of the air, and the fish of the sea, and whatever passes through the paths of the seas.
American King James Version×; 86:5; 100:1-5).
• It reveals that God's love is defined by His laws—by the two great laws of "Love God with all your heart, soul and mind" and "Love your neighbor as yourself" (Mark 12:29-31 Mark 12:29-31  And Jesus answered him, The first of all the commandments is, Hear, O Israel; The Lord our God is one Lord:
 And you shall love the Lord your God with all your heart, and with all your soul, and with all your mind, and with all your strength: this is the first commandment.
 And the second is like, namely this, You shall love your neighbor as yourself. There is none other commandment greater than these.
American King James Version×; Deuteronomy 6:5 Deuteronomy 6:5And you shall love the LORD your God with all your heart, and with all your soul, and with all your might.
American King James Version×; Leviticus 19:18 Leviticus 19:18You shall not avenge, nor bear any grudge against the children of your people, but you shall love your neighbor as yourself: I am the LORD.
American King James Version×). The Ten Commandments, and the statutes and judgments based on those commandments, show us how to live God's way of love.
• It reveals that sin brings suffering—that when we sin, there is a penalty. And if an entire nation sins, it eventually will reap the results of those sins. On the other hand, if an individual or a nation repents of sin and asks God for forgiveness, He is ready and willing to forgive (Deuteronomy 28:15-68 Deuteronomy 28:15-68  But it shall come to pass, if you will not listen to the voice of the LORD your God, to observe to do all his commandments and his statutes which I command you this day; that all these curses shall come on you, and overtake you:
 Cursed shall you be in the city, and cursed shall you be in the field.
 Cursed shall be your basket and your store.
 Cursed shall be the fruit of your body, and the fruit of your land, the increase of your cows, and the flocks of your sheep.
 Cursed shall you be when you come in, and cursed shall you be when you go out.
 The LORD shall send on you cursing, vexation, and rebuke, in all that you set your hand to for to do, until you be destroyed, and until you perish quickly; because of the wickedness of your doings, whereby you have forsaken me.
 The LORD shall make the pestilence stick to you, until he have consumed you from off the land, where you go to possess it.
 The LORD shall smite you with a consumption, and with a fever, and with an inflammation, and with an extreme burning, and with the sword, and with blasting, and with mildew; and they shall pursue you until you perish.
 And your heaven that is over your head shall be brass, and the earth that is under you shall be iron.
 The LORD shall make the rain of your land powder and dust: from heaven shall it come down on you, until you be destroyed.
 The LORD shall cause you to be smitten before your enemies: you shall go out one way against them, and flee seven ways before them: and shall be removed into all the kingdoms of the earth.
 And your carcass shall be meat to all fowls of the air, and to the beasts of the earth, and no man shall fray them away.
 The LORD will smite you with the botch of Egypt, and with the tumors, and with the scab, and with the itch, whereof you can not be healed.
 The LORD shall smite you with madness, and blindness, and astonishment of heart:
 And you shall grope at noonday, as the blind gropes in darkness, and you shall not prosper in your ways: and you shall be only oppressed and spoiled ever more, and no man shall save you.
 You shall betroth a wife, and another man shall lie with her: you shall build an house, and you shall not dwell therein: you shall plant a vineyard, and shall not gather the grapes thereof.
 Your ox shall be slain before your eyes, and you shall not eat thereof: your ass shall be violently taken away from before your face, and shall not be restored to you: your sheep shall be given to your enemies, and you shall have none to rescue them.
 Your sons and your daughters shall be given to another people, and your eyes shall look, and fail with longing for them all the day long; and there shall be no might in your hand.
 The fruit of your land, and all your labors, shall a nation which you know not eat up; and you shall be only oppressed and crushed always:
 So that you shall be mad for the sight of your eyes which you shall see.
 The LORD shall smite you in the knees, and in the legs, with a sore botch that cannot be healed, from the sole of your foot to the top of your head.
 The LORD shall bring you, and your king which you shall set over you, to a nation which neither you nor your fathers have known; and there shall you serve other gods, wood and stone.
 And you shall become an astonishment, a proverb, and a byword, among all nations where the LORD shall lead you.
 You shall carry much seed out into the field, and shall gather but little in; for the locust shall consume it.
 You shall plant vineyards, and dress them, but shall neither drink of the wine, nor gather the grapes; for the worms shall eat them.
 You shall have olive trees throughout all your coasts, but you shall not anoint yourself with the oil; for your olive shall cast his fruit.
 You shall beget sons and daughters, but you shall not enjoy them; for they shall go into captivity.
 All your trees and fruit of your land shall the locust consume.
 The stranger that is within you shall get up above you very high; and you shall come down very low.
 He shall lend to you, and you shall not lend to him: he shall be the head, and you shall be the tail.
 Moreover all these curses shall come on you, and shall pursue you, and overtake you, till you be destroyed; because you listened not to the voice of the LORD your God, to keep his commandments and his statutes which he commanded you:
 And they shall be on you for a sign and for a wonder, and on your seed for ever.
 Because you served not the LORD your God with joyfulness, and with gladness of heart, for the abundance of all things;
 Therefore shall you serve your enemies which the LORD shall send against you, in hunger, and in thirst, and in nakedness, and in want of all things: and he shall put a yoke of iron on your neck, until he have destroyed you.
 The LORD shall bring a nation against you from far, from the end of the earth, as swift as the eagle flies; a nation whose tongue you shall not understand;
 A nation of fierce countenance, which shall not regard the person of the old, nor show favor to the young:
 And he shall eat the fruit of your cattle, and the fruit of your land, until you be destroyed: which also shall not leave you either corn, wine, or oil, or the increase of your cows, or flocks of your sheep, until he have destroyed you.
 And he shall besiege you in all your gates, until your high and fenced walls come down, wherein you trusted, throughout all your land: and he shall besiege you in all your gates throughout all your land, which the LORD your God has given you.
 And you shall eat the fruit of your own body, the flesh of your sons and of your daughters, which the LORD your God has given you, in the siege, and in the narrow place, with which your enemies shall distress you:
 So that the man that is tender among you, and very delicate, his eye shall be evil toward his brother, and toward the wife of his bosom, and toward the remnant of his children which he shall leave:
 So that he will not give to any of them of the flesh of his children whom he shall eat: because he has nothing left him in the siege, and in the narrow place, with which your enemies shall distress you in all your gates.
 The tender and delicate woman among you, which would not adventure to set the sole of her foot on the ground for delicateness and tenderness, her eye shall be evil toward the husband of her bosom, and toward her son, and toward her daughter,
 And toward her young one that comes out from between her feet, and toward her children which she shall bear: for she shall eat them for want of all things secretly in the siege and narrow place, with which your enemy shall distress you in your gates.
 If you will not observe to do all the words of this law that are written in this book, that you may fear this glorious and fearful name, THE LORD THY GOD;
 Then the LORD will make your plagues wonderful, and the plagues of your seed, even great plagues, and of long continuance, and sore sicknesses, and of long continuance.
 Moreover he will bring on you all the diseases of Egypt, which you were afraid of; and they shall stick to you.
 Also every sickness, and every plague, which is not written in the book of this law, them will the LORD bring on you, until you be destroyed.
 And you shall be left few in number, whereas you were as the stars of heaven for multitude; because you would not obey the voice of the LORD your God.
 And it shall come to pass, that as the LORD rejoiced over you to do you good, and to multiply you; so the LORD will rejoice over you to destroy you, and to bring you to nothing; and you shall be plucked from off the land where you go to possess it.
 And the LORD shall scatter you among all people, from the one end of the earth even to the other; and there you shall serve other gods, which neither you nor your fathers have known, even wood and stone.
 And among these nations shall you find no ease, neither shall the sole of your foot have rest: but the LORD shall give you there a trembling heart, and failing of eyes, and sorrow of mind:
 And your life shall hang in doubt before you; and you shall fear day and night, and shall have none assurance of your life:
 In the morning you shall say, Would God it were even! and at even you shall say, Would God it were morning! for the fear of your heart with which you shall fear, and for the sight of your eyes which you shall see.
 And the LORD shall bring you into Egypt again with ships, by the way whereof I spoke to you, You shall see it no more again: and there you shall be sold to your enemies for slaves and bondwomen, and no man shall buy you.
American King James Version×; Psalms 103:8-13 Psalms 103:8-13  The LORD is merciful and gracious, slow to anger, and plenteous in mercy.  He will not always chide: neither will he keep his anger for ever.  He has not dealt with us after our sins; nor rewarded us according to our iniquities.  For as the heaven is high above the earth, so great is his mercy toward them that fear him.  As far as the east is from the west, so far has he removed our transgressions from us.  Like as a father pities his children, so the LORD pities them that fear him.
American King James Version×).
• It reveals the plan of God—that there would be a Savior who would pay the death penalty for your sins and my sins; that this Savior, the Messiah, would establish the Kingdom of God on earth; and that there would be a resurrection of the dead to eternal life (Isaiah 53; Daniel 2:44 Daniel 2:44And in the days of these kings shall the God of heaven set up a kingdom, which shall never be destroyed: and the kingdom shall not be left to other people, but it shall break in pieces and consume all these kingdoms, and it shall stand for ever.
American King James Version×; 7:27; 12:2-3; Job 14:14-15 Job 14:14-15  If a man die, shall he live again? all the days of my appointed time will I wait, till my change come.  You shall call, and I will answer you: you will have a desire to the work of your hands.
American King James Version×; Ezekiel 37).
• It reveals that there would be a new covenant under which God would give people the gift of His Spirit, which would remove our heart of stone and replace it with a heart that would love and obey God (Jeremiah 31:31-34 Jeremiah 31:31-34  Behold, the days come, said the LORD, that I will make a new covenant with the house of Israel, and with the house of Judah:
 Not according to the covenant that I made with their fathers in the day that I took them by the hand to bring them out of the land of Egypt; which my covenant they broke, although I was an husband to them, said the LORD:
 But this shall be the covenant that I will make with the house of Israel; After those days, said the LORD, I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people.
 And they shall teach no more every man his neighbor, and every man his brother, saying, Know the LORD: for they shall all know me, from the least of them to the greatest of them, said the LORD: for I will forgive their iniquity, and I will remember their sin no more.
American King James Version×; Ezekiel 36:26-27 Ezekiel 36:26-27  A new heart also will I give you, and a new spirit will I put within you: and I will take away the stony heart out of your flesh, and I will give you an heart of flesh.  And I will put my spirit within you, and cause you to walk in my statutes, and you shall keep my judgments, and do them.
American King James Version×).
• It reveals that humanity is created in God's image, created to be like Him and to share rulership with God over the entire universe (Genesis 1:26-27 Genesis 1:26-27  And God said, Let us make man in our image, after our likeness: and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing that creeps on the earth.
 So God created man in his own image, in the image of God created he him; male and female created he them.
American King James Version×; Psalms 8:6 Psalms 8:6You made him to have dominion over the works of your hands; you have put all things under his feet:
American King James Version×, Hebrews 2:6-8 Hebrews 2:6-8  But one in a certain place testified, saying, What is man, that you are mindful of him? or the son of man that you visit him?  You made him a little lower than the angels; you crowned him with glory and honor, and did set him over the works of your hands:  You have put all things in subjection under his feet. For in that he put all in subjection under him, he left nothing that is not put under him. But now we see not yet all things put under him.
American King James Version×).
These are some of the wonderful truths that the Old Testament reveals. It's no wonder that Satan has blinded the minds of people into thinking that it's obsolete, irrelevant or something that God had to discard because He had a better idea. The New Testament is built on the foundation of the Old. Together they form one complete story—the story of God's deep love for mankind and His plan for humanity. GN