If there is only "one baptism", why do we practice water baptism for believers?

In light of Ephesians 4:5, why do we practice water baptism?

The reasoning behind this question seems to be that "one baptism" is the baptism of the Spirit (Acts 1:5; 1 Corinthians 12:13) and therefore Christians have no other baptism - no water baptism.

Two possible responses to this depend on how we interpret "one baptism." Some base their interpretation on the grouping they see in the seven "one things" in Ephesians 4:4-6. The first three form a group: one Body, one Spirit (Who formed the Body), one hope (belonging to the Body, see 1:18). The next three form a group: one Lord (Whom all obey), one faith (by which all have trusted Christ or one body of revealed truth which all keep by obedience), one baptism (by which all have expressed their union with Him). The last is one God and Father of all. The first may be positional (what God has done), the second practical (what we are to do), the third theological and sums up the previous groups. If we accept this interpretation, the one baptism is water baptism which God has ordained for every believer in this age.

There may be reason, however, to view the one baptism as the baptism of the Spirit. The words, "There is" at the beginning of verse 4 are supplied by the translators. The words may obscure the connection of verses 4 through 6 with verse 3. Paul is expanding his statement, "the unity of the Spirit." At Pentecost, the Spirit formed a unique entity that had never existed before. That unity, the subject of the mystery (ch 3), is composed of both Jews and Gentiles (ch 1, 2). In these verses, Paul sums up the positional teaching of the previous chapters. He uses it as the pivot on which he bases his practical exhortation ("endeavoring to keep . . .").

The one Lord is the One in Whom all are united and, anticipating the rest of the epistle, Whom all are to obey. The one faith is the revealed body of truth, now including the mystery regarding the Church. The one baptism is the one event that formed the Body. Apart from this interpretation, Paul would be speaking about the unity of the Spirit without mentioning when the Spirit formed it. If that is the interpretation of "one baptism," in these three verses (vv 4-6), Paul is dealing with our position (what God has done for us). That baptism will never be repeated and does not take place when a believer is saved. The Lord said it would take place not many days after He was with His disciples (Acts 1:5). Paul teaches that water baptism expresses our union with Christ (Romans 6:4, 5) and it is our practical responsibility to be baptized. Further, the Lord associates baptism with discipleship and the message of the gospel in this age (Matthew 28:19, 20; Mark 16:15, 16). He also indicates that the believer is responsible to be baptized and that is done not by the Spirit but by those who "go," "make disciples," "baptizing them," "teaching them" (Matthew 28:19, 20).

D. Oliver