Regarding this matter of rewards, we are in error if we believe we must never seek rewards. Some think that serving with an eye to a reward is crass and mercenary, even when the reward comes from God. Why not give just to give? Such a view comes from a mistaken understanding. The rewards that God gives are not ribbons or medals but actually something of himself.
C. S. Lewis explained it perfectly:
We must not be troubled by unbelievers when they say that this promise of reward makes the Christian life a mercenary affair. There are different kinds of reward. There is the reward which has no natural connexion with the things you do to earn it, and is quite foreign to the desires that ought to accompany those things. Money is not the natural reward of love; that is why we call a man a mercenary if he marries a woman for the sake of her money. But marriage is the proper reward for a real lover, and he is not mercenary for desiring it… The proper rewards are not simply tacked on to the activity for which they are given, but are the activity itself in consummation.
Preaching the Word – Preaching the Word – The Sermon on the Mount: The Message of the Kingdom.