In Thoughts on Religious Experience, Archibald Alexander (founder of Princeton Seminary) asks why spiritual growth is so slow in us. He gives 4 reasons; here is the first.
First, there is a defect in our belief of the freeness of divine grace. To exercise unshaken confidence in the doctrine of gratuitous pardon is one of the most difficult things in the world; and to preach this doctrine fully without verging towards antinomianism is no easy task, and is therefore seldom done. But Christians cannot but be lean and feeble when deprived of the proper nutriment. . . . the doctrine of free grace, without any mixture of human merit, is the only true object of faith. Christians are too much inclined to depend on themselves, and not to derive their life entirely from Christ. There is a spurious legal religion, which may flourish without the practical belief in the absolute freeness of divine grace, but it possesses none of the characteristics of the Christian's life. . . . even when the true doctrine is acknowledged, in theory, often it is not practically felt and acted on. . . . Here, I am persuaded, is the root of the evil; and until religious teachers inculcate clearly, fully, and practically, the grace of God as manifested in the gospel, we shall have no vigorous growth of piety among professing Christians. (201-02)