Exactly! The letters of Paul were not written a priori. This is where both Luther and Calvin went wrong. They are meant ONLY to support, clarify, and reinforce the contents of the Synoptic Gospels. That alone was Paul's mission. They are not stand alone additions, revisions, extensions or new revelations and not to be used out of the context of the Synoptic Gospels.
Whether by recounting Jesus’ life or application of the prophetic scriptures, it was the unfolding of what the good news was that Peter said even the angels were desirous of peering into. (1 Peter 1:10-12)
Not Luke's good news or Paul's, etc., but one gospel.