Overall meaning : Believers! Shall I direct you a highly profitable transaction that will save you from a painful punishment? It is to believe in Allah and His Messenger, Muhammad (may Allah bless him and grant him peace), and fight against His enemies with your wealth and with your persons to make His religion reign supreme. That would be best for you, if you but knew it.
If you do so, Allah will forgive you your sins and admit you into Gardens beneath which rivers flow, and fine palaces in gardens of perpetual abode. Such reward is indeed the greatest success. He will also grant you another thing that you dearly love: help from Allah and a speedy victory. Proclaim the good news of such great reward, Muhammad, to the faithful.