“And said, Verily I say unto you, Except ye be converted, and become as little children, ye shall not enter into the kingdom of heaven.”
And said: truly, I say to you, unless you turn and become like children, you shall never enter the kingdom of heaven. The conversion that the kingdom requires: turning and becoming like children. The turning (strepho) is the word of repentance — a directional change from the disciples' current orientation. The unless communicates the absolute necessity of the change: the greatness-seeking orientation cannot enter the kingdom; it must be turned from.