Neither baptism nor any other work is required for one to be justified, but rather faith in God who justifies the ungodly apart from works (Rom. 4:5). Several reasons can be offered for separating baptism from justification.
First, Peter affirmed that Cornelius had already received the Holy Spirit before he baptized him (Acts 10:47; see also Rom. 8:9). Second, Paul was clearly justified before he was baptized (Acts 9:1-18; 22:6-16). Third, the Ethiopian eunuch was baptized as a result of his faith in Christ, not as a condition for being justified (Acts 8:26-40). Fourth, if baptism is required for salvation, then baptism is an essential part of the gospel. But Paul apparently did not think so, for he explicitly tells the Corinthians that “Christ did not send me to baptize, but to preach the gospel,” effectively separating the two (1 Cor. 1:17).
But water baptism is far from being an option when it comes to obedience to Christ. No one can consider himself a disciple of Christ who has not publicly identified himself with Christ in water baptism (Matt. 28:19). Baptism “saves” us in the same way that the waters of the Flood “saved” Noah and his family (1 Pet. 3:20-21). Noah was saved through water, not by water. He, like everyone else, is saved by faith alone (Heb. 11:6-7). But, as Noah’s obedience was a condemnation to the unbelieving, rebellious antediluvian world, so our obedience in baptism, an answer of a good conscience toward God, is a condemnation to the rebellious present world that rejects the death and resurrection of the Son of God. By publicly testifying to our faith by water baptism, we are “washing ourselves” of our identification with this cursed world system, and instead, identifying ourselves with the only Lord and Savior, Jesus Christ.