Let me see if I got this right God can tell someone to do something and then that person can have faith he can’t have faith unless God told him "So then faith comes by hearing, and hearing by the word of God. " Rom 10:17. If that person doesn't act on what God told them then that is sin?So Paul clearly taught that some acts which are not sin for some people ARE sin for anyone who cannot act in faith when they do such things.
God doesn't always tell people to do the same things so everyone doesn't have to have faith on the same things (except the essentials, Jesus is God, etc..). Now on the essentials God told everyone so everyone has to have faith in those things. So the truth is God does give words for individuals that may not apply for all mankind and it still is true because of that "I" facture mentioned earlier, true for the person who got the word but not necessarily for everyone.
Does that make sense?
Thanks
Sam