Paul is referring to a heretical custom whereby living Christians were baptized for the dead and unbaptized relatives or friends, who were supposed thus to be saved by proxy. Church Fathers make several references to such a practice, quoting the custom of the Marcionite heretics (Tertullian Against Marcion v. 10; On the Resurrection of the Flesh 48; Chrysostom Homilies on 1 Corinthians xl. 1).
It is not possible for Christians to be baptized vicariously on behalf of deceased relatives and friends. This is apparent from the many Scriptures which declare that a man must personally believe in Christ and confess his sins in order to profit by baptism and be saved “Then Peter said to them, “Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit” (Acts 2:38; also 8:36, 37; cf. Eze. 18:20–24; John 3:16; 1 John 1:9).
Even the most righteous of men can “deliver but their own souls” (Eze. 14:14, 16; Ps. 49:7). And death marks the close of human probation (Ps. 49:7–9; Eccl. 9:5, 6, 10; Isa. 38:18, 19; Luke 16:26; Heb. 9:27, 28).
In His service,