After Peter was granted to lead his sheep, he end up going against Christ word and end up going astray to follow those who were against Christ according to verse Galatians 2:11-21.
READ:
Paul Opposes Peter
Galatians 2:11-21 When Peter came to Antioch, I opposed him to his face, because he was clearly in the wrong. Before certain men came from James, he used to eat with the Gentiles. But when they arrived, he began to draw back and separate himself from the Gentiles because he was afraid of those who belonged to the circumcision group. The other Jews joined him in his hypocrisy, so that by their hypocrisy even Barnabas was led astray.
When I saw that they were not acting in line with the truth of the gospel, I said to Peter in front of them all, “You are a Jew, yet you live like a Gentile and not like a Jew. How is it, then, that you force Gentiles to follow Jewish customs?
“We who are Jews by birth and not ‘Gentile sinners’ know that a man is not justified by observing the law, but by faith in Jesus Christ. So we, too, have put our faith in Christ Jesus that we may be justified by faith in Christ and not by observing the law, because by observing the law no one will be justified.
“If, while we seek to be justified in Christ, it becomes evident that we ourselves are sinners, does that mean that Christ promotes sin? Absolutely not! If I rebuild what I destroyed, I prove that I am a lawbreaker. For through the law I died to the law so that I might live for God. I have been crucified with Christ and I no longer live, but Christ lives in me. The life I live in the body, I live by faith in the Son of God, who loved me and gave himself for me. I do not set aside the grace of God, for if righteousness could be gained through the law, Christ died for nothing!”
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Have you guys read the book of Galatians before? It teaches that the Galatians were relying on circumcision in which no one is saved by being circumcised according to Paul's words. Also, the Galatians were observance of the law, but they did not uphold the law by obeying it. They were relying on their works alone rather than faith in Jesus Christ due to the fact that they rejected the message of the cross since the message of the cross is about dying to the flesh (i.e., putting sin to death). They found the message of the cross to be foolish. That is what the whole book teaches. This is why they had no faith, because they received the gospel in vain by not believing in God's Son "Jesus Christ."