Originally Posted by Barnes

There are two words in the New Testament translated "repentance," one of which denotes a change of mind, or a reformation of life; and the other, sorrow or regret that sin has been committed. The word used here is the former, calling the Jews to a change of life, or a reformation of conduct. In the time of John, the nation had become extremely wicked and corrupt, perhaps more so than at any preceding period. Hence, both he and Christ began their ministry by calling the nation to repentance.

Originally Posted by Clarke

Repent - Μετανοειτε. This was the matter of the preaching. The verb μετανοεω is either compounded of μετα, after, and νοειν to understand, which signifies that, after hearing such preaching, the sinner is led to understand, that the way he has walked in was the way of misery, death, and hell. Or the word may be derived from μετα after, and ανοια, madness, which intimates that the whole life of a sinner is no other than a continued course of madness and folly: and if to live in a constant opposition to all the dictates of true wisdom; to wage war with his own best interests in time and eternity; to provoke and insult the living God; and, by habitual sin, to prepare himself only for a state of misery, be evidences of insanity, every sinner exhibits them plentifully. It was from this notion of the word, that the Latins termed repentance resipiscentia, a growing wise again, from re and sapere; or, according to Tertullian, Resipiscentia, quasi receptio mentis ad se, restoring the mind to itself: Contra Marcion, lib. ii. Repentance, then, implies that a measure of Divine wisdom is communicated to the sinner, and that he thereby becomes wise to salvation. That his mind, purposes, opinions, and inclinations, are changed; and that, in consequence, there is a total change in his conduct. It need scarcely be remarked, that, in this state, a man feels deep anguish of soul, because he has sinned against God, unfitted himself for heaven, and exposed his soul to hell. Hence, a true penitent has that sorrow, whereby he forsakes sin, not only because it has been ruinous to his own soul, but because it has been offensive to God.