I found this website of a Catholic having a discussion with Protestants on this verse:
socrates58.blogspot.com/2007/02/1-corinthians-1529-and-baptism-for-dead.html
**St. Francis de Sales:
Code:
This passage properly understood evidently shows that it was the custom of the primitive Church to watch, pray, fast, for the souls of the departed. For, firstly, in the Scriptures to be baptized is often taken for afflictions and penances; as in Luke 12:50 . . . and in St. Mark 10:38-9 . . . -- in which places Our Lord calls pains and afflictions baptism [cf. Matthew 3:11, 20:22-3, Luke 3:16].
This then is the sense of that Scripture: if the dead rise not again, what is the use of mortifying and afflicting oneself, of praying and fasting for the dead? And indeed this sentence of St. Paul resembles that of 2 Maccabees 12:44: "It is superfluous and vain to pray for the dead if the dead rise not again. . . ." Now it was not for those in Paradise [heaven], who had no need of it, nor for those in hell, who could get no benefit from it; it was, then, for those in Purgatory. Thus did St. Ephraim [d.373] expound it.**
I’m not sure of your comparison between proxy baptism and prayer to Mary and other canonized saints. The idea behind that is that as a Church, we are a communion of saints. Therefore, all Catholics are termed “saints”. On earth, we can ask our earthly saints, like parents, friends, etc., to pray for us. So, I could ask my roommate to pray for me that I pass a test, or something like that. Since we believe that death was destroyed by Christ, the Church, being the Body of Christ, is eternal, and extends beyond this earthly life. Therefore, we can not only ask earthly saints to pray for us, but Heavenly saints as well. Those on earth, in Purgatory, and in Heaven are still part of the Body of Christ, the Church. This is the reasoning (very basic) behind why we pray “to” Mary and the saints, asking them to pray for us.
What I think you were referring to is prayer FOR the dead, as in those in Purgatory. While there may be some basic similarities between that practice and proxy baptism, there are some important differences. With proxy baptism (and other proxy ordinances), one is attempting to change the salvation of the dead. Of course, they must choose to accept or reject it, however they are attempting to change what happens to the dead (or more appropriately, the dead, by accepting or rejecting the proxy ordinances, can change what happens to their souls).
With Catholic prayer for the dead, the salvation of the soul in question is already set. Prayer for the dead is only effective for those that are in Purgatory, and thus will go to Heaven after purification. Thus, all in Purgatory are already going to Heaven. There is nothing to change about that. We do believe that the “time” of purification can be shortened through prayer for the dead, Masses for the dead, and indulgences. So, we do not believe that one can be “saved” after death if they are not already saved. We do believe that if someone is being purified before Heaven, we can pray for those in Purgatory that they may have the vision of God sooner.