CIC 526 To become a child in relation to God is the condition for entering the kingdom.1 For this, we must humble ourselves and become little. Even more: to become “children of God” we must be “born from above” or “born of God”.2 Only when Christ is formed in us will the mystery of Christmas be fulfilled in us.3 Christmas is the mystery of this “marvelous exchange”:
O marvelous exchange! Man’s Creator has become man, born of the Virgin. We have been made sharers in the divinity of Christ who humbled himself to share our humanity.4

CIC 2367 Called to give life, spouses share in the creative power and fatherhood of God.5 “Married couples should regard it as their proper mission to transmit human life and to educate their children; they should realize that they are thereby cooperating with the love of God the Creator and are, in a certain sense, its interpreters. They will fulfill this duty with a sense of human and Christian responsibility.”6

1 Cf. Mt 18:3-4.
2 Jn 3 7; 1:13; 1:12; cf. Mt 23:12.
3 Cf. Gal 4:19.
4 LH, 1 January, Antiphon I of Evening Prayer.
5 Cf. Eph 3:14; Mt 23:9.
6 GS 50 # 2.