The following excerpts are from:
Peter S. Williamson, Ephesians (Catholic Commentary on Sacred Scripture; Grand Rapids, Mich.: Baker Academic, 2009)
Union with Christ, by water baptism, as a central theme in Ephesians
Union of believers with Christi. In various ways the letter repeatedly indicates that the benefits Christians enjoy are a result of their being united to Christ in the past (baptism), present, and future (2:5-7). (p.20)
On Eph 4:6
6. We share one baptism, that is, we have all been “baptized into Christ” (Rom 6:3-8; Gal 3:27-28; Col 2:12-13). By means of this baptism, we died and rose with Jesus and were joined to his body, the Church. Just as Christians are headed toward the same destination, the same “hope,” so we share the same point of origin, baptism. (p. 111)
On Eph 5:26
The Apostle explains why the heavenly bridegroom sacrificed himself for the Church in terms of three overlapping purposes. First, he did so to sanctify her, cleansing her by the bath of water with the word. To sanctify means to make holy, to set someone or something apart from what is profane and to quality that person or object for God’s presence. The means Jesus uses, to cleanse and sanctify the members of the Church is baptism, “the bath of water” (see Acts 22:16; 1 Cor 6:11; Titus 3:5). The last phrase, “with the word” (“by the word,” NRSV), might refer to the gospel message (Eph 1:13; John 15:2; 17:17), the profession of faith made by the newly baptized (Rom 10:9-10), or the formula used in baptism. Paul is saying Jesus offered his life as a sacrifice so that through the word of God and baptism we could become the kind of people fit for God’s presence.
In both the Jewish and Greek cultures of that time, the immediate cosmetic preparation of the bride included a bath with fragrant oils so that she could be as clean and beautiful as possible. Baptism, Paul is saying, is the Church’s bridal bath that prepares her to be united to her bridegroom. That it is Christ who bathes his bride is unique, because washing the bride is the job not of the bridegroom but of female servants or family members. It recalls Jesus’ humility and love expressed in his washing the feet of the disciples (John 13:1-17). By cleansing his bride through his death on the cross, Jesus placed himself in a lower position (Phil 2:6-8) and served her; in doing so he provided an example for husbands of how to “be subordinate” (5:21) and serve their wives. (pp. 166-67, emphasis in original)
