Paul’s formula for unity in Ephesians 4:5 is helpful because of its balance: there is one faith, one Lord, one baptism (+ one Eucharist) — that is to say, there is the content of the faith, the way it is lived out under Christ’s lordship, and the sacramental boundaries drawn around the church. All three are important ingredients in our unity. The objectivity of the covenant matters, but nothing objective guarantees subjective faithfulness. Unity has both objective and subjective elements.