Why does God act on behalf of believers?
God acts on behalf of believers because everything He does is in light of the resurrection. If there were no resurrection from the dead, there would be no reason to place believers into the body of Christ or to bother with them at all. The resurrection gives purpose and meaning to God's work on their behalf.
Les explains that the Holy Spirit through the Apostle Paul is addressing why God would do anything on behalf of the believer if there is no resurrection from the dead. He points to 1 Corinthians 12:13, where believers are baptized by one Spirit into one body, placed into the body of Christ by an act of God. If there is no resurrection, why should God even bother to place us into the body of Christ? Everything would become vanity and futile. God does everything in the light of resurrection, so the resurrection is the reason He acts on behalf of believers.
Else what shall they do which are baptized for the dead, if the dead rise not at all? why are they then baptized for the dead?