Paul's wrote letters to the churches which he had founded
trying to rectify the errors in their ways,
the errors in their lifestyles,
or misunderstandings.

Not all of the letters attributed to Paul in the Bible came from his hand.
Scholars only support his authorship of seven of the fourteen;
First Thessalonians, Galatians,1 and 2 Corinthians
Philipians, Philemon, and Romans.

It can be seen that even these seven have been heavily edited
to incorporate later concepts of the embryo church.
We have no copies dated earlier than
a century after they were written.
ample time for "corrective" action!
(much the same could be said of the Gospels, of course)
In his letters Paul refers consistently to the Gospel that he preached.
It can only be assumed that this was what he described in Romans (about 56AD).
Paul argues that believers can be assured of their hope in salvation,
having been freed from the bondage of sin by putting their faith in Jesus.
This promise is open to everyone since everyone has sinned.
Jesus' death on the cross makes believers dead to the law.
(but believers in what?)