You didn't.
Paul said.....
If anyone else thinks he may have confidence in the flesh, I more so: circumcised the eighth day, of the stock of Israel, of the tribe of Benjamin, a Hebrew of the Hebrews; concerning the law, a Pharisee; concerning zeal, persecuting the church; concerning the righteousness which is in the law, blameless. But what things were gain to me, these I have counted loss for Christ. Yet indeed I also count all things loss for the excellence of the knowledge of Christ Jesus my Lord, for whom I have suffered the loss of all things, and count them as rubbish, that I may gain Christ
Paul counted all of that as rubbish. I can imagine him saying to Peter, "it's a shame you don't know Christ, because I consider what you have as rubbish."
You see, this sums up mad totally. You are trying to explain a gospel that Paul considers rubbish, because it puts confidence in the flesh, and you're trying to say that it was legitimate back then :chuckle: