Saint Hilary of Poitiers: “Harden not your hearts"

Take care, brothers and sisters,
that none of you may have an evil and unfaithful heart,
so as to forsake the living God.

-- Heb 3:7-14

Through Baptism the Christian is sacramentally assimilated to Jesus, who in his own baptism anticipates his death and resurrection. The Christian must enter into this mystery of humble self-abasement and repentance, go down into the water with Jesus in order to rise with him, be reborn of water and the Spirit so as to become the Father's beloved son in the Son and "walk in newness of life":

Let us be buried with Christ by Baptism to rise with him; let us go down with him to be raised with him; and let us rise with him to be glorified with him. (St Gregory of Nazianzus, Oratio. 40, 9: PG 36, 369.)

Everything that happened to Christ lets us know that, after the bath of water, the Holy Spirit swoops down upon us from high heaven and that, adopted by the Father's voice, we become sons of God. (St Hilary of Poitiers, In Matth. 2,5: PL 9, 927.)

-- CCC 537