The New Testament begins with four gospels, each of which gives an account of the life of the Lord Jesus Christ. Next comes the Book of Acts, a history of the early church and a record of the acts of the Holy Spirit through Christ’s apostles after His resurrection. Finally there are twenty-two epistles (or letters) which represent the correspondence of the apostles and other early church leaders with new and struggling Christians, both fledgling churches and individuals. The first nine of these epistles were written by the apostle Paul to various churches he had founded. The letters are not presented in the order in which they were written but by looking with prayer and care, the reason for their order becomes clear.
The gospel of Christ is centered at the cross and that is also where our salvation begins. The cross is the central point of Christian doctrine, for without the cross there would be no salvation. Paul’s first four church epistles, as presented in the New Testament (Romans, 1 and 2 Corinthians, and Galatians) emphasize Christ and the cross. In these letters, Paul calls his readers to look to the cross to understand Christ’s sacrifice and what it means. The stress is upon one’s individual personal relationship to Christ through the cross. This is basic Christian doctrine that every believer should know.
Paul’s next three epistles as they appear in the Bible are Ephesians, Philippians, and Colossians. These all place an emphasis upon Christ and the church. Christ is the reconciler of all men to God, giving us peace and access to the Father, and bringing us into the body of believers, the church. Thus, these three epistles stress not only an individual's personal relationship to Christ but also his or her relationship to others in the body of Christ, the church. It is through the fellowship of the church that believers may be strengthened in their faith.
Paul’s final two epistles written to churches are 1 and 2 Thessalonians. The emphasis in these is Christ’s coming, the blessed hope of every believer. At His coming, He will take us to Himself as the perfecter of our salvation (see Hebrews 2:2). “In the two Thessalonian letters, the doctrine of the Cross and of the Church is presented very simply; but the wonderful prospect of the Lord’s return is elucidated in relation to His church as nowhere else in the New Testament” (J. Sidlow Baxter, Explore the Book). It is the hope of His return that strengthens our faith as we wait for Him.
So you see that the order in which the church epistles were placed in our Bibles is with sound reason and for the benefit of those who pick up God’s Book to read and study. First we are introduced to the doctrine of the cross, then to the fellowship of the church, and lastly to the consummation at Christ’s coming -- a very orderly order indeed!
I hope this information was helpful to you, as it was to me.
And may God bless you to overflowing as you faithfully study His word.