The earliest letters of Paul, and thusly, the earliest parts of the New Testament are his letters to the Church in Thessalonika. They are brief and direct and hold a lot of the marks of Paul’s latter writings. It is shocking, at least for me, to imagine early and later writings of Paul. Yet if you read 1 Thessalonians and then Romans, you can see a clear development of ideas.
Now what must be said clearly and firmly is that just because Paul develops his theology does not make any letter less than Scripture. Each is holy and God-Breathed. There are many ways of reading Scripture. One powerful of studying Paul’s journeys more is seeing how Paul was a person like we are. Paul was not special on his own. Paul was made special through grace. Paul was made an apostle through grace.
The Pastoral Epistles, 1 Timothy, 2 Timothy, and Titus are almost universally acknowledged as not being written by Paul the Apostle but by one of his students. This is only problematic if your view of the holiness of Scripture has more to do with Paul than God. 2 Timothy 3:16 is the verse often used to explain what Scripture is. Pseudonymous authorship was common in the ancient world even up to the early modern period. We do not read them because of how great the writers were but because God is here.
But as for you, man of God, shun all this; pursue righteousness, godliness, faith, love, endurance, gentleness. Fight the good fight of the faith; take hold of the eternal life, to which you were called and for which you made the good confession in the presence of many witnesses. In the presence of God, who gives life to all things, and of Christ Jesus, who in his testimony before Pontius Pilate made the good confession, I charge you to keep the commandment without spot or blame until the manifestation of our Lord Jesus Christ, which he will bring about at the right time—he who is the blessed and only Sovereign, the King of kings and Lord of lords. It is he alone who has immortality and dwells in unapproachable light, whom no one has ever seen or can see; to him be honor and eternal dominion. Amen. (1 Timothy 6:11-16)