Sanctifying grace: the essence of the spiritual life

"Sanctifying grace is the essence of the spiritual life from its earliest stages to its full unfolding. As its name indicates, it is a gratuitous gift of God, Who, by His own free and merciful will makes mortal men sharers in His divine life.

This divine life is out of all proportion to human nature and its exigencies; yet, when offered it respects all the claims of the freedom and the personal dignity of man.

This is how the gift of God is at once a life-giving reality (it is at the root of the supernatural life) and a fact of life (it works within, not outside of, the vital egg and flow of the creature's freedom and responsibility). This is also why the Christian is capable of merit and personal sanctity.

It is by becoming a reality most intimately personal to a man and by working in him as a principle of divine life that sanctifying grace is directed towards action"

-- Everything is Grace by Fr Anastasius of the Holy Rosary, ocd