Why are Paul's writings in the Bible?

[LinuxGal]

Too many historical factors to take into consideration, but roughly speaking it partly has to do with Paul being one of the prominent leaders among the mid-first century Christians, and had quite a number of epistles written in his name - some of which he himself didn't write but nevertheless were accepted/believed as such by later Christians.

What evidence is there that a "Paul" was a prominent leader among "First Century Christians" ?

The Jerusalem Church was destroyed in 70 CE, Shimon (the Lord's other brother) took the remnant over the Jordan, and only Paul's network of Gentile churches was left standing to write the histories and define orthodoxy.