In this passage, Paul moves from talking about what Christ has done for us to what we must do by the Spirit.
Unity in the Body of Christ
4:1 I therefore, a prisoner for the Lord, urge you to walk in a manner worthy of the calling to which you have been called, 2 with all humility and gentleness, with patience, bearing with one another in love, 3 eager to maintain the unity of the Spirit in the bond of peace. 4 There is one body and one Spirit—just as you were called to the one hope that belongs to your call— 5 one Lord, one faith, one baptism, 6 one God and Father of all, who is over all and through all and in all. (ESV)