Observe in Luke 2:40 what clear proof we have that the Lord Jesus was really and truly man as well as God. We read that when Mary and Joseph returned to their own city Nazareth, "the child grew and became strong."
There is, doubtless, much that is deeply mysterious in the Person of the Lord Jesus. How the same Person could be both perfect God and perfect man is a point that necessarily goes beyond our understanding.
One thing, however, is perfectly clear, and we would do well to lay firm hold upon it. Our Lord experienced everything that belongs to man's nature - except only sin. As man He was born an infant. As man He grew from infancy to boyhood. As man He yearly increased in bodily strength and mental power, during His passage from boyhood to adulthood. Of all the sinless conditions of man's body - its feebleness as a child, its growth, its regular progress to maturity - He was in the fullest sense a human being. We must rest satisfied with knowing this. To pry beyond is useless. To know this clearly is of much importance. An absence of settled knowledge of it has led to many wild heresies.
One comforting, practical lesson stands out, something we should never overlook. Our Lord is able to sympathize with humanity in every stage, from the cradle to the grave. He knows by experience the nature and temperament of the child and the youth and the adult. He has stood in their place. He has occupied their position. He knows their hearts. Let us never forget this in dealing with young people concerning their souls. Let us tell them confidently that there is One in heaven at the right hand of God who is exactly suited to be their Friend. He who died on the cross was once a youth Himself and feels a special interest in youth, as well as in adults.
Adapted from The Gospel of Luke by J.C. Ryle (Chapter 2).