If baptism saves, then why did Jesus save the thief on the cross without telling him to be baptized?
Baptism does in fact save us (1 Pet. 3:21; Mark 16:16). In order for anyone who is not a Christian to become a Christian and have their sins forgiven, they must be baptized (Acts 2:38-39). In order to be added to the body of Christ which is his church, one must be baptized (1 Cor. 12:13; cf. Acts 2:41, 47). In order to put on Christ and be clothed in him and buried with him to rise to a new life, one must be baptized (Gal. 3:27; Rom. 6:3-4; cf. John 3:3-5).
So why was the thief on the cross saved by our Lord without being given the opportunity to be baptized?
The “one baptism” (Eph. 4:4-6) commanded in the New Covenant is a baptism “into Christ’s death” (Rom. 6:3). When Jesus told the penitent thief that he would join him in Paradise on that very day, Christ obviously had not died yet (Lk. 23:39-43). In fact, by virtue of his death having not yet occurred, the New Covenant which commands baptism for salvation was not yet in place and in force. We know this because the writer of Hebrews, while discussing the New Covenant, brought out that it could not go into effect until after the death of the one who made it, just like any other last will and testament (Heb. 9:15-17). This is why Paul brought out that the Old Covenant, the Law of Moses, was broken down and abolished “through the cross” (Eph. 2:14-16), that Jesus had “nailed it to the cross” (Col. 2:14). It was only after his resurrection had taken place that Jesus had given the command to be baptized in order to be saved (Mk. 16:16; Matt. 28:19). When Jesus told the thief he would join him in Paradise (implying that the thief was saved), they both were still living under the Old Covenant.
Jesus, being the Son of God, certainly had the power to forgive the penitent thief and thus save him (cf. Lk. 5:18-26; 7:36-50). This he did, without requiring baptism on the thief’s part since that command would not be given until after he died and rose again. We live under the New Covenant, in the time since he gave the command for one to believe, repent, and be baptized in order to be saved and have forgiveness of sins.
With that in mind, have you been baptized into Christ?