Christ says that unless we’re converted, and become as little children, we can’t go to Heaven. (Mt 18:3) Whatever salvation is, according to Jesus, it includes becoming childlike.
The context of His teaching was a dispute among the disciples about which of them would be the greatest in Christ’s earthly kingdom, and granted the most privilege and power. (Lk 9:46) The disciples were evidently making comparisons among themselves, trying to exalt some over others, vying for position. Christ tells them that unless they’re changed in the core of their nature, free of such comparison and self-exaltation, they aren’t going to make it into His kingdom at all. In other words, the disciples, at this point in time, are yet unregenerate: lost. Their pride gives them away.
This isn’t the first time the topic has surfaced; in His initial recorded teaching, Christ tells us the poor in spirit own the kingdom of God: they comprise it — all those in the kingdom are poor in spirit, and all the poor in spirit are in the kingdom. Unless pride begins to die in us, until humility begins to flourish in us, and we’re esteeming others better than ourselves, nothing of Heaven can live in us.
Christ continues in His analogy by saying those who humble themselves to become more like little children are the greatest in His kingdom. (Mt 18:4) This relates to a parallel concept: those who obey all of God’s laws and teach others to do the same, are considered great in the kingdom. (Mt 5:19) For both to be true, the two concepts must be equivalent in some way.
Small children tend to be free of pride, haughtiness and ambition; they naturally feel inclined to look up to and emulate their elders; they aren’t preoccupied with judging others, comparing themselves with others, or posing and posturing to be more than they are. They know they’re utterly dependent on others to care for them, and tend to be trusting, not suspicious or jaded. When properly disciplined and loved, young children tend to be obedient and faithful. In these same ways, those who come to God in salvation acknowledge their utter dependence on Him, trust Him and believe on Him, taking Him at His Word, obeying Him and seeking to be close to Him.