I think the commonality that ties all Christians together is the Apostle’s Creed and Nicene Creed. If they are part of your Church your Church is Christian.
Do you realize that Fred Thompson belongs to a restorationist Christian church which rejects the post-apostolic creeds. As do many other Christian denominations.
Even St. Athanasias of Athanasian creed fame was branded a heretic.
Commonality that ties all Christians together is Jesus Christ. We don’t repeat the creeds, but we certainly do love and worship the Lord Jesus Christ.