The way that CS Lewis puts this is essentially that if the reward becomes the motive, you're not going to get it:
> We are afraid that heaven is a bribe, and that if we make it our goal we shall no longer be disinterested. It is not so. Heaven offers nothing that a mercenary soul can desire. It is safe to tell the pure in heart that they shall see God, for only the pure in heart want to. There are rewards that do not sully motives.
> We are afraid that heaven is a bribe, and that if we make it our goal we shall no longer be disinterested. It is not so. Heaven offers nothing that a mercenary soul can desire. It is safe to tell the pure in heart that they shall see God, for only the pure in heart want to. There are rewards that do not sully motives.