On several occasions Jesus of Nazareth is plainly called a man. Unlike the English language, the Greek tongue has two terms for man. One is anthropos, which merely means a man as representative of the human species.

The second Greek word, aner, means a man solely as a male human. Both words are used to describe Jesus Christ.

Many years after the resurrection of Jesus Christ, how did the apostle Paul refer to Him?

"For there is one God and one Mediator between God and men, the Man [Greek anthropos] Christ Jesus" (1 Timothy 2:5 1 Timothy 2:5For there is one God, and one mediator between God and men, the man Christ Jesus;
American King James Version×).

Any understanding of Jesus Christ's role and purpose must be based on this historic fact. Jesus' manhood was full and complete (Philippians 2:5-8 Philippians 2:5-8 [5] Let this mind be in you, which was also in Christ Jesus: [6] Who, being in the form of God, thought it not robbery to be equal with God: [7] But made himself of no reputation, and took on him the form of a servant, and was made in the likeness of men: [8] And being found in fashion as a man, he humbled himself, and became obedient to death, even the death of the cross.
American King James Version×) in the sense that He lived a life as a physical human being—He became hungry and ate, got tired and rested and walked and talked just like any other man. (The book of Hebrews fully attests to Christ's existence as a human being. It would be well worth your time to read and meditate on the book of Hebrews from this perspective.)

As a man, Jesus had nothing in His appearance to distinguish Him from other men of His time (Isaiah 53:2 Isaiah 53:2For he shall grow up before him as a tender plant, and as a root out of a dry ground: he has no form nor comeliness; and when we shall see him, there is no beauty that we should desire him.
American King James Version×). The essential difference was in the realm of the spiritual. Unlike any other member of the human species (Ecclesiastes 7:20 Ecclesiastes 7:20For there is not a just man on earth, that does good, and sins not.
American King James Version×; Romans 3:23 Romans 3:23For all have sinned, and come short of the glory of God;
American King James Version×), Jesus Christ never sinned (compare Hebrews 4:15 Hebrews 4:15For we have not an high priest which cannot be touched with the feeling of our infirmities; but was in all points tempted like as we are, yet without sin.
American King James Version×; 1 Peter 2:22 1 Peter 2:22Who did no sin, neither was guile found in his mouth:
American King James Version×). He carried out His Father's will perfectly!

What did Jesus accomplish during His short lifetime on earth?

"Men of Israel, hear these words: Jesus of Nazareth [was] a Man [Greek aner] attested by God to you by miracles, wonders, and signs which God did through Him in your midst, as you yourselves also know" (Acts 2:22 Acts 2:22You men of Israel, hear these words; Jesus of Nazareth, a man approved of God among you by miracles and wonders and signs, which God did by him in the middle of you, as you yourselves also know:
American King James Version×).

Though Jesus was truly a man, a physical human being, yet He came forth from God. God was His Father and the Holy Spirit the agent of procreation. He was miraculously conceived and born of a virgin (Mary) of the line of King David. Luke 3 contains His maternal genealogy. His legal genealogy (through Joseph) is found in the first chapter of Matthew. Truly Jesus Christ is both the Son of Man and the Son of God.

What was one of the biggest heresies that threatened the first-century Church?

"...Every spirit that does not confess that Jesus Christ has come in the flesh is not of God. And this is the spirit of the Antichrist, which you have heard was coming, and is now already in the world" (1 John 4:3 1 John 4:3And every spirit that confesses not that Jesus Christ is come in the flesh is not of God: and this is that spirit of antichrist, whereof you have heard that it should come; and even now already is it in the world.
American King James Version×; compare 2 John 1:7 2 John 1:7For many deceivers are entered into the world, who confess not that Jesus Christ is come in the flesh. This is a deceiver and an antichrist.
American King James Version×).

Denying Jesus Christ's humanity leads people away from the truth of God. If He had not been truly human, then His sacrifice for our sins would be null and void. Yet this same heresy that afflicted the early Church persists even to this day, creating doubt and confusion as to Jesus Christ's true nature and role.