The work of the Jesus in bringing about unity is seen in the title he has, which is Lord or Sovereign. There can only be one ultimate Lord, for by definition it means a person who has unrivalled authority. Since Jesus is Lord of the church, it means that everyone in it is a servant. When they see each other as servants of Christ, then they will have unity.
Paul mentions two other aspects of Christ’s work that bring about unity – faith and baptism. The term ‘faith’ can have an objective meaning and a subjective meaning. Objectively, it refers to the set of beliefs that Christians have; subjectively, it refers to the trust that believers have in Jesus. Both meanings stress unity, whether it is unity regarding what we believe as Christians or unity regarding the Saviour we believe in.
Probably Paul is referring to both ideas; Hendricksen, who favours subjective faith, comments that ‘the subjective and the objective cannot be separated: when a person surrenders himself to Christ as his Lord he at the same time also accepts the body of truth with reference to him.’
Paul also mentions baptism when he refers to the contribution of Jesus to unity. Often when we think of baptism we wonder if Paul is referring to baptism with water or baptism with the Spirit. I doubt if that distinction would have crossed Paul’s mind because baptism with water symbolised baptism with the Spirit. Baptism instead was the mark that separated believers from the world. It was a badge that they all shared, that told everyone who they were. So it gave them a sense of unity.