Surah Hud, Ayat 8

Ayat 8. And if We delay the torment for them till a determined term, they are sure to say, "What keeps it back?" Verily, on the day it reaches them, nothing will turn it away from them, and they will be surrounded by (fall in) that at which they used to mock! 

Hazrat Abu Hurairah (May Allah be pleased with him) reported: The Messenger of Allah  [SAWW](PBUH) said, "He who observes optional prayer (Tarawih prayers) throughout Ramadan, out of sincerity of Faith and in the hope of earning reward will have his past sins pardoned.'' [Al-Bukhari Volume 3, Book 32, Number 226]. 

Lesson : We learn from this Hadith that Qiyam in the month of Ramadan is a much-stressed act and has great importance from the viewpoint of reward and award. The sins which are pardoned through it are minor sins because major sins are not forgiven unless one makes sincere repentance and compensates those whom he has wronged.