1 Corinthians 13:4

This is the standard both sides already agree on, which makes it a good place to stand rather than to argue. Paul is writing to a congregation that was fracturing into parties. The love he describes is not sentiment; it is the behaviour that holds people together when they disagree — patient, kind, not keeping account of injury, as the chapter goes on to say. Two applications. First, in the apostolic record this love is visible in what happened after conflict: Paul and Barnabas split in anger, and Paul later sent for Mark; Paul rebuked Peter publicly, and Peter later called him beloved brother. The reconciliations are on the record. Second, and more delicately, it is the measure to bring to the practice of cutting off contact with family members who have come to believe something different. Ask what verses 4 to 7 would look like applied to a son or a mother in that situation. Do not answer for them. Compare Galatians 5:23, 2 Timothy 4:11, Luke 15:5.