The apostles say some amazing things about baptism. By it, Paul says, we are united to Christ (1 Cor. 12:13; Rom. 6:2; Gal. 3:27) in His death, burial, and resurrection (Rom. 6:1-6). Thus, Peter says, “baptism now saves us” (1 Pet. 3:21). And Paul follows by saying that being washed in baptism brings us new life and renewal by the Spirit (Tit. 3:5). Thus, the washing of baptism both sanctifies and justifies us (1 Cor. 6:11).
How can they say these things? Everything depends upon the first thing – i.e. by baptism the Spirit unites us to Jesus and makes us members of His body.
If the Spirit unites us to Christ at baptism and if all spiritual blessings are ours in union with Christ (Eph. 1:3) then we can understand why the apostles can say what they say about baptism. Baptism saves because we are united to the Savior; baptism sanctifies because we are united to the Holy One; baptism justifies because we are united to the Just One; baptism brings new life because we are united to the One who is life (John 1:4; 1 John 1:1-3). Baptism is no bare human ritual. It is inseparably joined to the purpose of the Father, the Person and work of the Son, and the power of the Spirit.
Yet, there is mystery here. Not all who are baptized enter into eternal life. What gives?
Baptism doesn’t save us automatically by itself and alone. Rather, the Spirit by baptism unites us to Jesus (who is Life). And, all those baptized are required to abide in Him by a living faith, trusting in Him alone for salvation, confessing their sins, walking in joyful obedience, and living in gratitude for the grace of God shed abroad in their hearts through Jesus (John 15:1-6).
In other words, the union established by the Spirit between us and Jesus works like the union He establishes between a man and a woman in marriage. The two become one by the blessing of the Spirit (“what God has joined together . . .” Matt. 19:6) and by virtue of this are obligated to cleave to one another throughout all their days (Gen. 2:24). The union of husband and wife depends upon their mutual loyalty and persevering love. If one partner ceases to love the other and forsakes his mate for another, the marriage is destroyed. The union that was brought about by the Spirit and the new life that was created by Him by means of the wedding, dies.
In the same way, one who is united to Jesus and decides to forsake Him for another god, forfeits the blessings that were his in union with Jesus and ends up like the prodigal, destitute and deserted. This is exactly what happened to God’s son, Israel (1 Cor. 10:1-11).
Of course we know that since salvation is all of grace (i.e. not based upon human merit or works but a free gift of God, Eph. 2:8-9), if anyone perseveres in faith, that too is the gift of God. So to point to perseverance as a baptismal obligation is not to mix human works with God’s grace but simply to magnify the fullness of God’s grace. (more later)