Verily I say unto you, Whosoever shall not receive the kingdom of God as a little child, he shall in no wise enter therein. Observe the "verily" with which our Lord introduces these words. He here adds something which extends what he has just said to those who are, not literally, but figuratively, little children.
We must first receive the kingdom into our affections before we can really enter into it. It is as though Christ said, "It is not unworthy of my dignity to take little children into my arms and bless them, because by my benediction they become fit for the kingdom of heaven.
And if you full-grown men would become fit for my kingdom, you must give up your ambitious aims and earthly contests, and imitate the simple unworldly ways of little children. The simplicity of the little child is the model and the rule for every one who desires, by the grace of Christ, to obtain the kingdom of heaven.
Our Lord's whole action here is a great encouragement to the receiving of little children by Holy Baptism into covenant with him.