The Biblical text affirms that Jesus Christ was human. It does this indirectly, in that it never comes out and explains or states it as such, but by describing His life, it shows Him to have a normal human existence. He was born, grew physically, mentally, and socially, ate and drank, felt, loved, and experienced suffering. He was fully human right down to the fact that He was free to choose whether to follow God’s will or not. He was tempted. The only thing that differentiated Jesus from the rest of mankind was the fact that He resisted temptation. He never sinned. While this distinguishes Him from the rest of humanity, it does not make Him less human. In fact, the opposite is true. In living a sinless life, Jesus Christ was more human that any other person has ever been. He was the ideal and perfect human.
Since the Bible states that Jesus was human, the question remains: why? Why did the incarnation occur? Evidently it was necessary to bring the rest of humanity back to where God intended it to be. It was a necessary element in the Salvation plan of God. In the incarnation, Christ accomplished His goal on earth. He brought about the Atonement of humanity. To do this He needed to be God, for only God can save, but He nonetheless needed to be human, for it was humanity He came to save, and only a representative of the human race could pay the price required to free the race from sin.
This is why Jesus had to really be human. He could not just take on the form of a human, nor become partially human, nor simply clothe Himself in flesh. It was humanity He came to save, so humanity He had to become, not even simply generic humanity, but an individual human man, a real representative.