Sin: The Suicidal Action of the Human Will

In Tim Keller's excellent TGC11 talk, he quoted from W.G.T. Shedd's "Sin Is Spiritual Slavery," found in Sermons to the Natural Man (1871):

Sin is the suicidal action of the human will.

Shedd goes on:

To do wrong destroys the power to do right.

This is illustrated in the effect of a vicious habit in diminishing a man's ability to resist temptation.

But habit is the continual repetition of of wrong self-decisions, every one of which reacts upon the will as a faculty, and renders it less strong and energetic to good.

No man can do a wrong act, and be as sound in his will, and as spiritually strong, after it as he was before it.