In the beginning the desire is more clouded, the assent more languid, the obedience less intense, and these gifts must increase. But they grow in us not like lilies of the field but by trying, wrestling, seeking, asking, knocking, and "this is not of ourselves; it is the gift of God.” The Savior says in Matt. 13:12, “It will be given to him who has.” Whoever has received very small spiritual gifts from God should acknowledge them with a grateful mind, asked that they be increased, and neglect no opportunities to advance in piety. To him it will be given that he may be the richer, but from him who does not have, that is, from him who behaves as if he had received nothing from God, even what he has will be taken away.
This was taken from http://gottesdienstonline.blogspot.com/2013/04/gerhard-on-preaching-sanctification.html.