Repentance is beloved to Allah, as He says:
"Verily, Allah loves those who repent and those who purify themselves." [Al-Qur'an 2:222]
Repentance is an obligation on every believer. Allah says:
"O you who believe! Turn to Allah in sincere repentance!" [Al-Qur'an 66:8]
Repentance is from the means of attaining success. Allah says:
"And O believers, all of you, repent to Allah in order that you may be successful." [Al-Qur'an 24:31]
Success is when someone gets what he is looking for and is saved from what he is running from.
Through sincere repentance Allah forgives sins no matter how big they are and no matter how many they are. Allah says:
"Say: O My slaves who have transgressed against themselves (because of sins), do not despair from the mercy of Allah. Verily, Allah forgives all sins. Verily, He is All-Forgiving, Most Merciful." [Al-Qur'an 39:53]