or if God were not to exist, then simply God.
A god in many cases is as you describe. I'll only make a list of the commonalities shared among many gods, and you can be the judge. Gods:
- have power over us
- expect servility, worship, or praying to them
- lays down laws about which of our actions are forbidden, such as:
- which foods we may eat
- how we must treat other beings
- what actions one might take to earn favour from the god including:
- sacrifices, either materially or of self-abnegation/abstention
- looks after and protects us if we are good
The word "god" does double duty here because as a word it can also mean something that a person follows or holds in high-esteem. So:
4. One that is worshiped, idealized, or followed: Money was their god.
American Heritage Dictionary
So even disregarding god the transcendent power, you may say, to use your example sentence:
"Our limited lifetimes should be used in our service instead of us using it to serve the false god of materialism".
There's a line in the Bible that says no man can serve two masters:
Ye cannot serve God and mammon.
And here mammon is being used in the way I mentioned before, "mammon" meaning either money or:
2. avarice or greed
Collins English Dictionary
Using your other sentence, "We spend our entire lifetime serving an imaginary master". Riches and wealth are real things, but the pursuit of these things in the hope that they will make you happy may be elusive or imaginary, therefore, generally speaking, serving the god of riches and wealth is serving a false master, so to speak.
Feel free to tell me it makes no sense.