Ephesians 4:5

5.One Lord. In the first Epistle to the Corinthians, he employs the word Lord, to denote simply the government of God.

“There are differences of administration, but the same Lord.”
(1 Corinthians 12:5)

In the present instance, as he shortly afterwards makes express mention of the Father, he gives this appellation strictly to Christ, who has been appointed by the Father to be our Lord, and to whose government we cannot be subject, unless we are of one mind. The frequent repetition of the word one is emphatic. Christ cannot be divided. Faith cannot be rent. There are not various baptisms, but one which is common to all. God cannot cease to be one, and unchangeable. It cannot but be our duty to cherish holy unity, which is bound by so many ties. Faith, and baptism, and God the Father, and Christ, ought to unite us, so as almost to become one man. All these arguments for unity deserve to be pondered, but cannot be fully explained. I reckon it enough to take a rapid glance at the apostle’s meaning, leaving the full illustration of it to the preachers of the gospel. The unity of faith, which is here mentioned, depends on the one, eternal truth of God, on which it is founded.

One baptism, This does not mean that Christian baptism is not to be administered more than once, but that one baptism is common to all; so that, by means of it, we begin to form one body and one soul. But if that argument has any force, a much stronger one will be founded on the truth, that the Father, and Son, and Spirit, are one God; for it is one baptism, which is celebrated in the name of the Three Persons. What reply will the Arians or Sabellians make to this argument? Baptism possesses such force as to make us one; and in baptism, the name of the Father, and of the Son, and of the Spirit, is invoked. Will they deny that one Godhead is the foundation of this holy and mysterious unity? We are compelled to acknowledge, that the ordinance of baptism proves the existence of Three Persons in one Divine essence.