“Therefore we were buried with him through our baptism into his death, in order that, just as Christ was raised up from the dead through the glory of the Father, we also should likewise walk in a newness of life. For if we have become united with him in the likeness of his death, we shall certainly also be united with him in the likeness of his resurrection.”​—Ro 6:4, 5; 1Co 15:31-49.

Clarifying the matter still further, Paul, in writing to the congregation at Philippi, described his own course as “a sharing in [Christ’s] sufferings, submitting myself to a death like his, to see if I may by any means attain to the earlier resurrection from the dead.” (Php 3:10, 11) Only the Almighty God the heavenly Father, who is the Baptizer of those who are baptized in union with Jesus Christ and into his death, can complete the baptism. This He does through Christ by raising them up out of death to be united with Jesus Christ in the likeness of his resurrection, which is to heavenly, immortal life.​—1Co 15:53, 54.

In the context, 1 Corinthians 15:3, 4 shows that what is principally under discussion is belief in the death and resurrection of Jesus Christ. The following verses then present evidence of the soundness of that belief (vss 5-11); they discuss the serious implications of denying belief in the resurrection (vss 12-19), the fact that the resurrection of Christ gives assurance that others will be raised from the dead (vss 20-23), and how all of this works toward the unification of all intelligent creation with God (vss 24-28). Verse 29 obviously is an integral part of this discussion. But whose resurrection is at issue in verse 29? Is it the resurrection of the ones whose baptism is referred to there? Or is it that of someone who died before that baptism took place? What do the following verses indicate? Verses 30 to 34 clearly show that the future life prospects of living Christians are there being discussed, and verses 35 to 58 state that those were faithful Christians who had the hope of heavenly life.

That agrees with Romans 6:3, which says: “Do you not know that all of us who were baptized into Christ Jesus were baptized into his death?” As this scripture makes plain, that is not a baptism that a Christian undergoes on behalf of someone already dead but is, instead, something that affects the person’s own future.

In what sense, then, were those Christians “baptized for the purpose of being dead ones,” or “baptized into his death”? They were immersed into a course of life that was to lead them as integrity-keepers to death, as was the case with Christ, and with the hope of a resurrection like his to immortal spirit life. (Ro 6:4, 5; Php 3:10, 11) This was not a baptism that was accomplished quickly, as water immersion is. More than three years after his immersion in water, Jesus spoke of a baptism that was not yet completed in his own case and that was yet future for his disciples. (Mr 10:35-40) Since this baptism leads to resurrection to heavenly life, it must begin with the operation of God’s spirit on the person in such a way as to engender that hope, and it must end, not at death, but with realization of the prospect of immortal spirit life by means of the resurrection.​—2Co 1:21, 22; 1Co 6:14.

Likewise those who undergo Christian baptism become God’s property, his slaves, to employ as he sees fit. (1Co 6:20) An example of God’s direction of such matters is found in Revelation, where reference is made to a definite number of persons finally “sealed,” namely, 144,000. (Re 7:4-8) Even before such final approval, God’s holy spirit serves as a seal that gives those sealed a token in advance of their inheritance, a heavenly one. (Eph 1:13, 14; 2Co 5:1-5) Those having such a hope are also told: “God has set the members in the body [of Christ], each one of them, just as he pleased.”​—1Co 12:18, 27.