Grace is the very energies of God himself. The Orthodox Church believes that through the Trinitarian ministry of the Holy Spirit these energies are mediated to mankind. That is, how God acts in forgiving and spiritual healing. Grace is the working of God himself, not a created substance of any kind that can be treated like a commodity.
Def from my churches website:
GRACE - (Sl. Blahodat') The gift of God's own presence and action in His creation. Through grace, God forgives sins and transforms the believer into His image and likeness. Grace is not merely unmerited favoran attitude of God toward the believer. Grace is God's uncreated energy bestowed in the sacraments and is therefore truly experienced. A Christian is saved through grace, which is a gift of God and not a reward for good works. However, because grace changes a person, he or she will manifest the effects of grace through righteous living. (John 1:17; Rom. 5:21; Eph. 1:7; 2:8; 2 Thess. 1:12; 1 Pet. 5:5.)