Romans 6:1-2 portrays the opposition Paul faced, mostly from Jews, most of whom were NOT believers. Either way, your objection to the Gospel of the New Covenant of the Grace of Christ is the same objection they had against the revelation of God’s grace Paul had received from the Lord.
They weren't believers?! LOLOL The letter was written to the believers in Rome.
Romans 6:1-4
What shall we say, then? Shall we go on sinning so that grace may increase? 2 By no means! We are those who have died to sin; how can we live in it any longer? 3 Or don’t you know that all of us who were baptized into Christ Jesus were baptized into his death? 4 We were therefore buried with him through baptism into death in order that, just as Christ was raised from the dead through the glory of the Father, we too may live a new life.
I will not debate with you further. You twist to suit your premise.