Why would Jesus tell us to become like little children (Matt. 18:3)? Some use this as reason to say that children matter to God (which is true, although this text may not be the strongest to draw your argument from). Some look at it and remind us of the character of children—their propensity to love, trust and not be so darn cynical; their generally humble and teachable nature is what Jesus is getting at, they say (which again, is true).
But what adds power to this argument is the Incarnation, where Jesus—the One for whom, by whom and through whom all things exist, hold together and have their meaning (cf. Col. 1:16-17)—literally became a little child. Check out Doug Wilson’s take on it from God Rest Ye Merry:
…Jesus told us to become like little children. And what did He do in the Incarnation? He became a little child. The one, in short, who told us that we needed to be humbled, converted, and made like little children, was the same one who humbled Himself and took the form of a baby in the womb of a young maiden. Jesus told us to become like little children, but He did so as the one who had—in an utterly unique way—become a little child.
He, the eternal Word, the one who spoke the galaxies into existence, was willing to become a little baby boy who could do nothing with words except jabber, and in that jabbering, make glad his mother and earthly father. He, the source of all life and all nourishment for that life, was willing to be breastfed. He, the same one who had separated the night from the day, and had shaped the sun to rule the day, and the moon to rule the night, was willing to have his diapers changed for a year or so. It is not disrespectful to speak this way; for Christians, it is disrespectful not to. We believe in the Incarnation, in the Word made flesh. This is our glory; this is our salvation.
Jesus told us that in order to enter His kingdom, we would have to stoop. This is not surprising, because He was the one who stooped in a mystifying way in the creation of that kingdom. He stooped—the ultimate Word became a single cell, and then a cluster of cells, and then visibly a baby, although still less than a pound, and then a child who kicked his mother from inside, delighting her immeasurably. He became a little child, and then, years later, He told us to copy Him in this demeanor—to become little children.
Douglas Wilson, God Rest Ye Merry: Why Christmas is the Foundation for Everything (Kindle location 501)