When we think of the incarnation, it is important to remember that the Son of God took on, not merely human flesh, but everything it means to be human (except, of course, sin). Not only did Jesus possess a human body with all its weaknesses and limitations, but also a human mind with all its weaknesses and limitations. The way this was expressed in the Definition of Chalcedon in 451 AD was that "he has a rational soul and a body." As a man, Jesus was a normal human being.
It is easy to think of Jesus as merely a human body with divinity somehow poured into him, animating and controlling him. But this would make Jesus less than human. Instead, we understand that Jesus is fully human, possessing a human mind, human emotions, human limitations, and a human body, even while he remains fully God. This means that as a man Jesus was often ignorant of the same kinds of things we would be ignorant of, such as the timing of his return (Mark 13:32) or the identify of the one who touched him in a crowd (Mark 5:30).
The significance of the human mind of Jesus is often overlooked, but expressed beautifully by the modern theologian Donald Macleod:
"Christ had to submit to knowing dependently and to knowing partially. He had to learn to obey without knowing all the facts and to believe without being in possession of full information. He had to forego the comfort which omniscience would sometimes have brought. This, surely, was a potent factor in the dereliction (Mark 15:34). The assurance of the Father's love, the sense of his own sonship and the certainty of his victory were all eclipsed, and he had to complete his obedience as the one who walked in darkness, knowing only that he was sin and that he was banished to the outer darkness. He suffers as the one who does not have all the answers and who in his extremity has to ask, "Why?" The ignorance is not a mere appearing. It is a reality. But it is a reality freely chosen, just as on the cross he chose not to summon twelve legions of angels. Omniscience was a luxury always within reach, but incompatible with his rules of engagement. He had to serve within the limitations of finitude" (from "The Person of Christ").
The reality that Jesus has both a human mind and a human body makes the significance of the chorus of "O Holy Night" all the more powerful:
"He knows our need, to our weakness is no stranger; Behold your King!"