For he himself is our peace, who has made us both one and has broken down in his flesh the dividing wall of hostility, by abolishing the law of commandments expressed in ordinances, that he might create in himself one new man in place of two, so making peace. – Ephesians 2:14-15 (ESV)
You yourselves know how unlawful it is for a Jew to associate with or to visit anyone of another nation, but God has shown me that I should not call any person common or unclean. 29 So when I was sent for, I came without objection. I ask then why you sent for me. – Acts 10:28 (ESV)
To prevent our being perverted by contact with others or by mixing bad influences, (Moses) hedged us in on all sides with strict observances connected with meat and drink and touch and hearing and sight, after the manner of the law – Aristeas
Peter probably views this action as a tactically wise accommodation to the concerns of stricter Jewish Christians. Paul, however, sees the matter very differently. For him, Peter’s act sends the signal that Gentiles in Christ are not truly and fully cleansed from sin in Christ: that they remain morally stained and must be avoided; and that they can finally remove that stain only by themselves taking on Jewish customs. This is a flat contradiction to the truth of the gospel. – Doug Moo
We politely sit by “those other people” in church, but we won’t eat with them; we won’t really become friends with them. We won’t socialize with them, sharing our lives and homes and things with them. We will keep relationships formal and see them at official church meetings only.
All of this comes from not living in line with the gospel. Without the gospel, our hearts have to manufacture self-esteem by comparing our group with other groups. But the gospel tells us that we are all unclean without Christ, and all clean in him. – Tim Keller