Two gospels is simply is not what Paul is teaching, but true faith is manifest by what one does. For salvation is by faith, which is counted for righteousness, justifying the unGodly, but not a faith abstract from who Christ is, but one who "condemned sin in the flesh: That the righteousness of the law might be fulfilled in us, who walk not after the flesh, but after the Spirit. (Romans 8:4)
For Paul has been building his case in Rm. 2+3 that both Jews and Gentles are in need of salvation by faith said, thus he states in Rm. 3, "we have before proved both Jews and Gentiles, that they are all under sin;... (Romans 3:9ff) Being justified freely by his grace through the redemption that is in Christ Jesus: (Romans 3:24) See 120 and 162 and
As I see it, the doctrine at the beginning of the church was faith and the works that are included under the authority of the Jewish laws...
The law was righteous and those who kept the law became justified...
Paul revealed to this early church that a transition had taken place whereby Jesus is the only righteousness and belief in Jesus without the law replaced their earlier doctrine for justification...