Digits…checked!
Yup, nailed it. Anyone who is 100% service to others is a slave. This is the exact definition of slavery.
Ra didn't write the Law of One. It was channeled by multiple people purportedly from Ra, but we have all learned by now that these beings are mighty tricksters. So I think it's plausible that the being known as Ra was running a little game on the humans trying to channel him.
>hey let's see if we can get them to be voluntary slaves, that would be entertaining!
It's really not that far fetched.
I think a good guideline for balancing your service to others and service to self, is to remember that you cannot serve others well if you yourself are depleted. So looking out for #1 is always your first and needed step.