Failing to return Onesimus — a runaway slave — would have been a violation of the 7th Commandment.
An accurate synopsis of Philemon:
I am returning your runaway slave. Thank you for letting me use him for a time. Please do not beat him for stealing himself, etc. Remain firm in the faith.
PS. Please prepare a guest room for me.‹
“In God We Trust” is written on American currency not because America believes in God, but because money is the American god.