Grace is not a mere gift. It is God communicating His very life to us. Our creation by God is gratuitous. Grace is more. Much more. Grace moves us from a relation of slave and Creator to son and Father. Hence, it can only be given through Christ. His grace allows us to be sons with the Son and cry out to God, "Abba, Father!"
“Christian life is not mere friendship with God, not mere favor or acceptance. No, there are mysteries aglow here! Theology speaks with shy reverence and reserve of a ‘partaking in the divine nature.’ She sees in the life of grace an assimilation, a real, supernatural communion with God, which she calls physico-mystical…Grace is the appearing of God’s life in us. Created grace is the reflection of the uncreated grace which is God Himself. It is more than an elevation of being: since God gives Himself to the soul for its own, the soul is gripped by the heavenly notes that peal forth the canticle of grace within it. Grace is a vibrating in unison, a trembling and smouldering of the creature together with the divine music, holy and eternal, which rises in the august silence, the bright-darkness of the godhead; it rests truly therefore on a mysterious presence of God in us…With Cyril [of Alexandria] the Greek Fathers evolve a profound doctrine: that the sharing in God’s nature, the supernatural assimilation with God, grows as it were out of the insertion of our being in the life, the bosom of God. The Fathers recognize the full splendor of grace as a mysterious life-giving union of our being with the infinitely glorious life of God.”
-Julius Tyciak in Life in Christ.