The legalistic Jewish Christians were insinuating that Paul was sinning by eating with the Gentile believers. They had missed the wonder of the new covenant in Jesus' blood making Jew and Gentile one.
The old covenant and its demands along with pride in keeping the rules Paul declared crucified with Christ on the cross. Now, in place of the law, the Spirit reigns in us, the very life of Christ! His life in us helps us to live in the Spirit, which is something the laws of Moses could never do.