Both the internal evidence and external evidence support the fact that Paul wrote this letter to the Romans.
The external evidence comes from quotations and reminiscences of this epistle in Clement of Rome, Ignatius, Justin Martyr, Polycarp, Hippolytus, Marcion, the Muratori Canon, and the Old Latin and Syriac versions. From the time of Irenaeus onward the epistle was universally recognized as Pauline and canonical. The internal evidence of genuineness is also strong. The writer claims to be Paul (Rom 1:1) and makes personal references that can only be identified with the great apostle (cf. 11:13; 15:15-20). Style, argument, theology, and many other factors point to Pauline authenticity. At the beginning of the modern critical period a few Dutch, Swiss, and English scholars contested the authenticity of the book on the ground that the apostle was acquainted with so many individuals by name in a city where he had never been (see chapter 16). But this argument has been repeatedly shown to be weak because travel was extensive in Paul’s day, and he probably met these individuals elsewhere in the empire before they went to Rome to live (“Romans,” Unger’s Bible Dictionary).
Paul (Saul of Tarsus) was a Hebrew, Benjaminite, Pharisee, Roman Citizen, Persecutor of the Church, Apostle of Christ Jesus to the Gentiles. He was a thinker of the first order, a man with a penetrating mind, well-versed in the OT. A brilliant intellect, an iron will, and a compassionate heart made him the most effective apostle—”God’s chosen vessel.”
Just as God chose Moses to as the revelator of Israel for the Ten Commandments, and all connected with the Law dispensation; so Christ chose Saul of Tarsus as the revelator and unfolder of the truths connected with our Lord’s death, burial, and resurrection, and His ascended Person. And all the “mysteries” or “secrets” revealed to God’s people, in this dispensation by the Holy Spirit, are revealed through Paul. Finally, Paul is the unfolder of the great company of God’s elect, called the Church, the Body of Christ. Nevertheless, the apostle demonstrates from the OT that God is not finished with the nation of Israel.
Paul was converted without the intervention of human instrumentality, and was taught the Gospel by divine revelation—commissioned by Christ to be an apostle to the Jews and Gentiles. His natural character was ardent, energetic, uncompromising, and severe. Once saved, Paul was ready to submit to anything, and to yield everything for the spread of the Gospel.