This chapter starts off on a positive, encouraging note. God says, "When you have come into the land you are to inhabit..." (verse 2). This might seem odd on the heels of the last chapter. But remember that despite what had happened, God had stated that the younger generation would eventually enter Canaan. And in giving various commands regarding the making of grain and drink offerings in the land, He was also reaffirming that promise.
Verse 19 refers to a "heave" offering, a term that may sound strange to our ears. The word heave means "to lift up." It is thus the same as a wave offering. Here it is explained that the Israelites were to heave the first of each grain harvest. "Right at the beginning of the harvest, the harvester had to acknowledge that his produce was a gift from God. By holding up the very first produce from a harvest or the first cake made from the first grain of the season, the worshiper thanked God as the giver of all good gifts" (Nelson Study Bible, note on verse 17-21).
The chapter then moves on to the subject of sin. When someone got mixed up or forgot to perform a particular duty, such a sin of ignorance could be readily remedied. But deliberate sins, or sinning "presumptuously" (literally, "with a high hand")—in essence, defiantly shaking one's fist in God's face—was another matter entirely. It merited a severe penalty. Following in the chapter is an example of just such a situation—that of a man deliberately working on the Sabbath. The people didn't know how to deal with such a willful breaking of the commandment, so they temporarily incarcerated him until they could get instructions. The law already stated that he should die (Exodus 31:15 Exodus 31:15Six days may work be done; but in the seventh is the sabbath of rest, holy to the LORD: whoever does any work in the sabbath day, he shall surely be put to death.
American King James Version×), but not the means of death. God told Moses the man should die outside the camp of Israel at the hands of the people by stoning. This way all Israel would participate in and realize the severity of the punishment and the absoluteness of God's commandments. Today, no one is executed for Sabbath breaking. But God has already shown us His decreed penalty and exactly how He feels about the need to obey His laws. Indeed, the penalty for all sin is ultimately death (Romans 6:23 Romans 6:23For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord.
American King James Version×).
Man is not to seek after the things of his own heart, or his own eyes, or the pride of life, because those things are of the world (Numbers 15:39 Numbers 15:39And it shall be to you for a fringe, that you may look on it, and remember all the commandments of the LORD, and do them; and that you seek not after your own heart and your own eyes, after which you use to go a whoring:
American King James Version×; 1 John 2:16 1 John 2:16For all that is in the world, the lust of the flesh, and the lust of the eyes, and the pride of life, is not of the Father, but is of the world.
American King James Version×). Rather, we must forsake the spiritual harlotry of our old, sinful nature and set ourselves apart to follow only the true God (vNumbers 15:40-41 Numbers 15:40-41  That you may remember, and do all my commandments, and be holy to your God.  I am the LORD your God, which brought you out of the land of Egypt, to be your God: I am the LORD your God.
American King James Version×). We do not need to use tassels today as memory devices to remember all of God's laws, as God told the Israelites. Instead, God's Spirit writes His laws on our hearts and minds (Hebrews 8:10 Hebrews 8:10For this is the covenant that I will make with the house of Israel after those days, said the Lord; I will put my laws into their mind, and write them in their hearts: and I will be to them a God, and they shall be to me a people:
American King James Version×), helping us to remember all of His commands (John 14:26 John 14:26But the Comforter, which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatever I have said to you.
American King James Version×).