[It is that] you believe in Allāh and His Messenger and strive in the cause of Allāh with your wealth and your lives. That is best for you, if you only knew.
This profitable trade is that you have faith in Allah and His messenger, and you strive in His path (may He be glorified) by spending your wealth and giving your lives to seek His pleasure. That action is better for you if you know, so rush towards it.