Paul writes to them that he is astonished that they have allowed themselves to be misled by some other Christian evangelists: "Who are you listening to? Don't you realize that some people say that they're preaching the true gospel but they aren't even close?"
He issues an anathema against those he asserts are preaching a false gospel. He then asks a question that remains relevant to us: Whose approval is important to you? Do you care more about what the people around you think you should do or what God approves of? Are you trying to please people or Christ?
The difficulty that continues is the necessity of discerning God's will as it may different from that being espoused by some holy-appearing self-proclaimed paragons of Christians. Not everybody who claims the authority to tell us what we should be doing is really speaking the true gospel.