A. W. Tozer in an editorial he wrote for his denominational magazine, “The Futility of Regret”:
The human heart is heretical by nature. Popular religious beliefs should be checked carefully against the Word of God, for they are almost certain to be wrong.
Legalism, for instance, is natural to the human heart. Grace in its true New Testament meaning is foreign to human reason, not because it is contrary to reason but because it lies beyond it. The doctrine of grace had to be revealed; it could not have been discovered.
The essence of legalism is self-atonement. The seeker tries to make himself acceptable to God by some act of restitution, or by self-punishment or the feeling of regret. The desire to be pleasing to God is commendable certainly, but the effort to please God by self-effort is not, for it assumes that sin once done may be undone, an assumption wholly false. Long after we have learned from the Scriptures that we cannot by fasting, or the wearing of a hair shirt or the making of many prayers, atone for the sins of the soul, we still tend by a kind of pernicious natural heresy to feel that we can please God and purify our souls by the penance of perpetual regret….
Regret may be no more than a form of self-love. A man may have such a high regard for himself that any failure to live up to his own image of himself disappoints him deeply. He feels that he has betrayed his better self by his act of wrongdoing, and even if God is willing to forgive him he will not forgive himself. Sin brings to such a man a painful loss of face that is not soon forgotten. He becomes permanently angry with himself and tries to punish himself by going to God frequently with petulant self-accusations. This state of mind crystallizes finally into a feeling of chronic regret which appears to be a proof of deep penitence but is actually proof of deep self-love.
Regret for a sinful past will remain until we truly believe that for us in Christ that sinful past no longer exists. The man in Christ has only Christ’s past and that is perfect and acceptable to God. In Christ he died, in Christ he rose, and in Christ he is seated within the circle of God’s favored ones. He is no longer angry with himself because he is no longer self-regarding, but Christ-regarding; hence there is no place for regret.
A. W. Tozer, "The Futility of Regret." Captured in a book called That Incredible Christian, but the content is taken from editorials he wrote for the CMA magazine, Alliance Life Magazine. The compilation was assembled by one of the editors of the magazine, Anita M. Bailey