"You realize that St. Paul wrote his Letters before the Gospels were written?"
Well, there is scholarship that suggests that, but there's also scholarship that suggests differently. The bottom line is that we will never know, since the actual originals have disappeared.
The Christian scriptural canon is a funny thing. Learning how the New Testament came to be what it is today is a fascinating study. Theories abound regarding the source material.
One thing that's for sure is that it's the product of a committee. I sure wish I could be a mouse in the corner as its structure and content was decided. There's so much we don't know.
True. That committee is the Catholic Church, which canonized the Christian oral apostolic tradition.