I don't necessarily see Paul's writings as written specifically for the Hebrews, Romans, Colosians, Ephesians, Philippians, Thessalonians, and Corinthians. Paul was assigned the mission to deliver the gospel to everyone as was recorded in Acts 9:15 NKJV
"...he is a chosen vessel of Mine to bear My name before Gentiles, kings, and the children of Israel."
And since all the scripture is inspired of God is it trustworthy for our direction today. I believe God intended Paul's writing to be applied to our lives as well.
6 All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness,
17 that the man of God may be complete, thoroughly equipped for every good work.
2 Timothy 3:16, 17 NKJV