When a field has brought good, rich crops to perfect maturity, no one would logically say that the farmer made those fruits. Everyone would acknowledge that the crops had been produced by God. In the same way, our own perfection isn't brought about by inactivity and idleness, but by some activity on our part. Yet we aren't credited with its perfection. God is. He is the first and primary cause of the work. Take, for example, a ship that has overcome the dangers of the sea through hard working sailors, the aid of navigation, a pilot's zeal and carefulness, favorable breezes, and the careful observation of the signs of the stars. No one in his right mind would attribute the vessel's safety to anything else than the mercy of God when, after being tossed by the waves, and wearied by the billows, it has at last reached the harbor. Not even any of the sailors or the pilot would venture to say, "I have saved the ship," but would refer entirely to the mercy of God. This isn't because these men feel that they haven't contributed skill or labor to save the ship, but the vessel's safety was entrusted by God. Similarly, in the race of life, we must work diligently and passionately.
(From Day by Day with the Early Church Fathers, pg 175- Origen, First Principles 3.1)