Can someone serve two masters at one time?
There is a difference between being a slave of something and doing something.
Has someone ever asked you to do something and then you did it? Were you their slave?
Matthew 24:24 No man can serve two masters: for either he will hate the one, and love the other; or else he will hold to the one, and despise the other. Ye cannot serve God and mammon.
Are we not despising God when we willingly sin?