That Paul believed and accepted Jesus as his Lord and Savior, that he accepted his assignment to the Gentiles as from the Lord and his salutations describe his reverence to the Lord. In essence he was what he believed.
Romans 1:1-10
1 Paul, a servant of Jesus Christ, called to be an apostle, separated unto the gospel of God,
2 (Which he had promised afore by his prophets in the holy scriptures,)
3 Concerning his Son Jesus Christ our Lord, which was made of the seed of David according to the flesh;
4 And declared to be the Son of God with power, according to the spirit of holiness, by the resurrection from the dead:
5 By whom we have received grace and apostleship, for obedience to the faith among all nations, for his name:
6 Among whom are ye also the called of Jesus Christ:
7 To all that be in Rome, beloved of God, called to be saints: Grace to you and peace from God our Father, and the Lord Jesus Christ.