Galatians 3:26-28
26 For ye are all the children of God by faith in Christ Jesus.
27 For as many of you as have been baptized into Christ have put on Christ.
28 There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus.
Abridged Commentary - Galatians 3:27
3:27 In Romans 6:3-4, Galatians 3:27, and Colossians 2:12, the Apostle Paul speaks of being "baptized into Jesus Christ", and being "buried with (Jesus Christ) in baptism". In each case, it seems that this is either a reference to the baptism of the Spirit into the Body of Christ, mentioned in 1 Corinthians 12:12-13, which happens when a person believes in Jesus (Ephesians 1:12-14), or, it is the Apostle Paul expounding the symbolism of water baptism, which represents dying to oneself (Luke 9:23, Galatians 2:20), and walking in the newness of life secured by the death and resurrection of Jesus Christ.
The Grace New Testament Commentary - Galatians 3:27
3:27 This is one of the proof texts often used to teach baptismal regeneration. Yet it actually refutes it! According to the preceding verse, the sole condition of sonship is faith in Christ. Verse 27 further explains v 26 (note the explanatory gar at the beginning of the sentence).
The word translated "baptized" is a flexible one. It refers to being immersed, placed into, or identified with someone or something. All who have been placed into the Body of Christ by the baptism of the Holy Spirit are clothed with Christ and His righteousness!
This cannot be a reference to Christian water baptism for three reasons. First, there is no mention of water or anything related to water baptism in the context. Second, this verse is an explanation of the previous one. Third, if water baptism were a condition, then justification would not be simply by faith in Christ.