Paul, a slave of Christ Jesus, called to be an Apostle and set apart for the Gospel of God . . . to all the beloved of God in Rome, called to be holy. Grace to you and peace from God our Father and the Lord Jesus Christ. (Rom 1:1-7)
https://bible.usccb.org/bible/readings/101623.cfm
The oldest Christian writings were not the gospels but rather the letters. Saint Paul’s letter to the community of Rome was treasured, copied and then shared with other communities. Eventually these letters became the Scriptures we have today.