Matthew 18:4

ταπεινώσει ἑαυτόν. He who shall be most Christ-like in humility (see Philippians 2:7-8) shall be most like Christ in glory. Cp. ἐταπείνωσεν ἑαυτόν, γενομένος ὑπήκοος μέχρι θανάτου, θανάτου δὲ σταυροῦ. διὸ καὶ ὁ Θεὸς αὐτὸν ὑπερύψωσεν κ.τ.λ., Philippians 2:8-9. ταπεινώσει marks the particular point in which little children are an example to Christians, and the words of St Paul give the precise lesson of this incident taken in connection with the death upon the Cross just foretold. Jesus gives himself to His disciples as an example of ταπεινότης μέχρι θανάτου. See ch. Matthew 11:29.

The expression ταπειν. ἑαυτὸν is more emphatic than the middle voice and implies greater self-mastery.