John Wesley on Luke 17:10

When ye have done all, say, We are unprofitable servants - For a man cannot profit God. Happy is he who judges himself an unprofitable servant: miserable is he whom God pronounces such. But though we are unprofitable to him, our serving him is not unprofitable to us. For he is pleased to give by his grace a value to our good works, which in consequence of his promise entitles us to an eternal reward.