ok I see the dilemma..
Paul was preaching to the gentiles concerning the difference between law and faith.
Perhaps he was in his teaching mode and not all had turned to Christ but were questioning the difference.
There were many questions even Jesus' disciples were struggling with:
Mar 2:18
And the disciples of John and of the Pharisees used to fast: and they come and say unto him, Why do the disciples of John and of the Pharisees fast, but thy disciples fast not?
There are still many questions being answered even today, even though the answers can be found by seeking and asking.
Paul was a teacher, teaching. Not all the students perhaps were saved. And maybe they had questions.
That isn't to say that there weren't christians among the gentiles, that were gentiles themselves but yet were already born again.
Not everyone was saved at the same time. Many were still learning and questioning, some staying and some leaving.
Some understanding and some confused.
Thats my opinion.
Hugs