How do you know it wasn't written to Paul?. It starts off Paul ,called to be an Apostle. Someone could have been guiding Paul. Like a letter starts like Dear Bob, called to be a Teacher.
There is nothing that clarifies it's Paul who wrote it, but the scripture says Tertius wrote it. I, Tertius wrote this epistle.
I'm still not convinced.
Now I myself am confident concerning you, my brethren, that you also are full of goodness, filled with all knowledge, able also to admonish one another. Nevertheless, brethren, I have written more boldly to you on some points, as reminding you, because of the grace given to me by God,
that I might be a minister of Jesus Christ to the Gentiles, ministering the gospel of God,
that the offering of the Gentiles might be acceptable, sanctified by the Holy Spirit. Therefore I have reason to glory in Christ Jesus in the things which pertain to God. For I will not dare to speak of any of those things which Christ has not accomplished through me, in word and deed,
to make the Gentiles obedient— in mighty signs and wonders, by the power of the Spirit of God, so that from Jerusalem and round about to Illyricum I have fully preached the gospel of Christ.
And so I have made it my aim to preach the gospel, not where Christ was named, lest I should build on another man’s foundation, but as it is written:
“To whom He was not announced, they shall see;
And those who have not heard shall understand.”
For this reason I also have been much hindered from coming to you. But now no longer having a place in these parts, and having a great desire these many years to come to you, whenever I journey to Spain, I shall come to you. For I hope to see you on my journey, and to be helped on my way there by you, if first I may enjoy your company for a while.
But now I am going to Jerusalem to minister to the saints.
For it pleased those from Macedonia and Achaia to make a certain contribution for the poor among the saints who are in Jerusalem.
It pleased them indeed, and they are their debtors.
For if the Gentiles have been partakers of their spiritual things, their duty is also to minister to them in material things. Therefore, when I have performed this and have sealed to them this fruit, I shall go by way of you to Spain. But I know that when I come to you, I shall come in the fullness of the blessing of the gospel of Christ.
Now I beg you, brethren, through the Lord Jesus Christ, and through the love of the Spirit, that you strive together with me in prayers to God for me,
that I may be delivered from those in Judea who do not believe, and that my service for Jerusalem may be acceptable to the saints, that I may come to you with joy by the will of God, and may be refreshed together with you. Now the God of peace be with you all. Amen.
I commend to you Phoebe our sister, who is a servant of the church in Cenchrea, that you may receive her in the Lord in a manner worthy of the saints, and assist her in whatever business she has need of you; for indeed she has been a helper of many and of myself also.
Greet Priscilla and Aquila, my fellow workers in Christ Jesus,
who risked their own necks for my life, to whom not only I give thanks, but also all the churches of the Gentiles. Likewise greet the church that is in their house.
Greet my beloved Epaenetus, who is the firstfruits of Achaia to Christ. Greet Mary, who labored much for us. Greet Andronicus and Junia, my countrymen and my fellow prisoners,
who are of note among the apostles, who also were in Christ before me.
Romans 15:14-16:7
JLB