وَتَحْسَبُونَهُ هَيِّنًا وَهُوَ عِنْدَ اللَّهِ عَظِيمٌ
Watahsabūnahū hayyinan wahuwa ‘indallāhi ‘azīm
And you thought it to be a light matter, while it was most serious in the sight of Allah.
(Sūratun Nūr, No. 24, Āyat 15)
This verse is part of the passage that talks about a rumor spread about ‘Ā’ishah, the wife of the Holy Prophet (s). She was inadvertently left behind after an expedition and had to spend the night in the desert. The next morning she returned to Madinah with Safwān who was there at that time. The hypocrites started spreading rumors about the behavior of ‘Ā’ishah which were finally quelled by her maid who vouched for her.
The reproach in this verse is to those who spread rumors and think nothing of damaging the reputation of others. It can also be applied to all sins which are taken lightly. When a person sins, it is a disobedience to Allah. Even that which may be considered a small sin, it is still very serious and grave. The Holy Prophet (s) says: Do not look at the smallness of the sin, rather look at what you have dared to do (Wasā’il al-Shī‘ah, Chapter on Jihad of the Nafs).
A believer who considers Allah as great will naturally consider any disobedience to Him as grave and a very serious matter. Imam Ali (a) describes this beautifully: When you magnify [the seriousness of] a sin you have magnified Allah, and when you diminish [the seriousness of] a sin you have diminished Allah. For His right over you is in all small and large things. A great sin that you have magnified becomes small with Allah, the Elevated, and a small sin that you have diminished becomes great with Allah (Al-Ja’fariyyāt, p. 237).
What is meant by taking sins lightly?
a) Struggling to refrain from sins – Imam Hasan al-‘Askarī says: The strongest of those who struggle among mankind is the one who abandons sins (Tuhafal ‘Uqūl, p. 489).
b) Thinking seriously about one’s sins – The Holy Prophet (s) says: When Allah wishes good for His servant He places his sins in front of him, visible, the disobedience being heavy and bitter. And when He does not wish good for His servant He makes him forget his sins. (Makārimul Akhlāq, v. 2, p. 365).
c) Feeling stressed by one’s sins – The Holy Prophet (s) in an advice to Abū Dharr says: A believer sees his sins as a rock over his head that may fall on him while a disbeliever sees his sins as a fly that passes by his nose (Al-‘Āmālī by Shaykh al-Tūsī, p. 527).
One day the Holy Prophet (s) along with his companions came to a barren desert. It was time to eat and the Prophet told them to go in all directions to search for firewood. The companions looked around and said it would not be possible to find firewood in such a place. The Prophet told them to look for whatever they could find. Each of the companions started searching and when they returned they were able to put together a whole pile of firewood. It was enough to make a fire to cook their food. The Prophet looked at the pile and said: the sins of a believer are also like this pile of firewood. They are not apparent but when you look carefully you can find them. They can be gathered together and can become a large pile one day. (Dāstane Rastan, Shahid Mutahharī, v.1, p.174).
Use this verse to remind yourself of the seriousness of sins. Recite it when the thought of committing a sin flits through your mind. How can you dare? You may think it small but to Allah it is mighty.
Sources: http://www.tebyan.net/newindex.aspx?pid=152773
Āqā Mahdi Mirza Pūya/S.V. Mir Ahmed Ali, English Translation & Commentary of the Quran