Fulfilled from both sides

[In the Old Covenant, God] wills to be a father to his people, and desires his people to be his children. 'I will be your Father, and you will be my children. I am holy, therefore be you holy. Walk before me and be perfect.' [cf. Lev 26:12; 2 Sam 7:14; Lev 11:44; Gen 17:1]

[In sending his Son] God fulfils the covenant from the side of God, 'I will be your God, your Father', and fulfils the covenant from the side of man, 'I will be your obedient child'. This is the mighty act of the incarnation which is at once the act of God's humiliation and the act of man's exaltation, for he who in such amazing grace descended to make our lost cause his own, ascended in accomplishment of his task, elevating man into union and communion with the life of God.

(pp. 56-57, TF Torrance, The Incarnation)