Al-Maidah (The Repast):12

The Path to the Garden
"If you attend to your prayers, practise regular charity, believe in My messengers and support them and offer up to God a generous loan, I shall forgive you your sins and admit you into gardens through which running waters flow."

God does not give His blessings as a personal favour or a personal gift. This comes only after its conditions are fulfilled. This was true in this particular covenant God made with the Children of Israel.

The first condition was to attend to prayer. This is more than merely offering prayers. It means that prayers should become a manifestation of a true relationship between man and his Lord. Second was charitable payment, in recognition of God's favour for having given us what we have and by way of acknowledgement of the fact that whatever we may own actually belongs to God. The next condition was to believe in God's Messengers making no distinction between them. Every single one of them was sent by God to preach the same message.

In addition to zakat, giving generously to support God's cause is mentioned as a loan given to God. Since God has promised to return to man every penny that he spends in His way along with His reward, which will be several-fold, the Quran characterizes this spending as a loan to God.

To forgive someone's evil deeds signifies two things:

First, that if a man decides to follow the Straight Path and strives to follow God's directives in both thought and action his soul will be purged of many evils and his way of life will gradually become free of corruption.

Second, if, in spite of this reform, weaknesses still persist in a man's life he is assured that God will not punish him and will have his failing erased from his record.