Philo Judaeus Quod Deterius Potiori Insidiari Soleat 56

[56] So, when we say that piety is a ministering to God, we say that it is in some such a service as slaves discharge to their masters, who are taught to do without hesitation that which is commanded them; but, again, there will be a difference, because the masters are in need of service, but God has no such want. So that, in the case of the masters, the servants do supply that which will be of use to them, but to God they supply nothing beyond a mind imbued with a spirit of willing obedience; for they will not find anything which they can improve, since all things belonging to masters are, from the very beginning, most excellent; but they will benefit themselves very greatly by determining to become friends to God.