We read it in the Holy Qur'an :--

  "AND REPENT UNTO GOD ALL TOGETHER, O YOU

   BELIEVERS"! (24:31)

 This is why it is the consensus of the Nation (Ummah) that repentance is a duty. The Prophet, Sallallahu alaihi Wasallam, said that 'the one who repents from his sin is as the one who is sinless, repentance erases whatever has preceded it'.

Repentance is an immediate incumbent obligation, since the avoidance of sins and obedience to God are an unceasing duty. Note that repentance should immediately follow committing of sin, as postponement of repentance multiplies the sins for those who do not repent. This is not the same as the multiplication of good deeds, for not to repent is itself a sin, so that the failure to repent adds one sin upon another, the first being the original evil act and the second the absence of repentance. The 2 sins both require repentance, so that, if not forthcoming, they become 4 according to the same pattern. This is multiplication, but not the same as the multiplication of good deeds, for Allah Ta'ala says :--

 "Whoso brings a good deed shall have ten the like thereof,

  and whoso brings an evil deed shall only be recompensed 

  the like of it." (6:160)

If we examine our state/ourselves fairly, we would see that we need repentance more than we need food, water and shelter. This is because our sins are veiling us from beholding the Unseen and stand between us and the Beloved.