Again, a believer can only be rewarded when he is imprisoned unjustly. Many, many believers throughout the ages since Jesus Christ have been thrown into prison because of their faith. But, they not only persevered, they prospered spiritually. Many people have been reached for the Gospel within prison walls, because of the witness which the Christian inmate was able to provide. Also, Paul reported the phenomenon that his imprisonment was actively strengthened the believers on the outside.
Man can kill our physical bodies .
The physical martyrdom of the saints of God has always been the catalyst for church growth. God literally turns the evil which wicked men do to the Christian saints into the highest good, namely, heavenly rewards for their faithfulness. Immediately upon death, the Christian saint passes into Paradise, to be comforted in the bosom of Jesus Christ. So, if Christians do not fear persecution, prison, or physical death, we have no reason not to be relaxed and happy in our secure trust in Jesus Christ. We can literally enjoy each day which God has given us.