He fell, step by step
It is easy, therefore, to understand how any of these children of God might be moved from his own steadfastness, and yet the great truth of God, declared by the apostle, remain steadfast and unshaken. He did not keep himself by that grace of God which was sufficient for him. He fell, step by step. First into negative, inward sin, not stirring up the gift of God which was in him (2 Timothy 1:6), not watching toward prayer (1 Peter 4:7), not pressing on to the mark of the prize of his high calling (Philippians 3:14). Then into positive inward sin, inclining to wickedness with his heart, giving way to some evil desire or temper. Next he lost his faith, his sight of a pardoning God, and consequently his love of God. And being then weak, and like another man, he was capable of committing even outward sin.
1771 text
It is easy therefore to understand, how any of these children of God might be moved from his own stedfastness, and yet the great truth of God, declared, by the apostle, remain stedfast and unshaken. He did not keep himself, by that grace of God which was sufficient for him. He fell, step by step, first into negative, inward sin, not stirring up the gift of God which was in him, not watching unto prayer, not pressing on to the mark of the prize of his high calling: then into positive inward sin, inclining to wickedness with his heart, giving way to some evil desire or temper. Next, he lost his faith, his sight of a pardoning God, and consequently his love of God. And being then weak and like another man, he was capable of committing even outward sin.