Allah says:

[مَّنْ عَمِلَ صَـلِحاً فَلِنَفْسِهِ]

(Whosoever does righteous good deed, it is for himself;) means, the benefit of which will come to him.

[وَمَنْ أَسَآءَ فَعَلَيْهَا]

(and whosoever does evil, it is against himself.) means, the consequences of that will come back on him.

[وَمَا رَبُّكَ بِظَلَّـمٍ لِّلْعَبِيدِ]

(And your Lord is not at all unjust to (His) servants) means, He only punishes people for their sins, and He does not punish anyone except after establishing proof against him and sending a Messenger to him.