Q My husband died in April of this year after a three-year battle with cancer. At the wake, the priest asked us to pray for his soul. Other than, "May he rest in peace," what prayers are meaningful? C., Melville
A Most of our prayers are for the living. We pray they'll be healed if they are ill. We pray to be forgiven for our sins, and we pray to give thanks to God for the myriad blessings showered upon us in our lifetime.
Praying for the dead compels our belief that death is not the end of us if we are comprised of both bodies and souls. However, the idea of a soul and of a life for the soul after death does not appear in the early books of the Hebrew Bible.
The earliest reference to praying for the dead does not appear until the very late book of II Maccabees, when Judah Maccabee prays over his slain comrades in the war against the Seleucid Greeks. He prayed over them because he discovered each of them had been wearing a pagan amulet to the gods of Jamnia, which was a prohibited act of idolatry. The prayers were meant to atone for their sins and help them enter heaven: "For if he were not expecting that those who had fallen would rise again, it would have been superfluous and foolish to pray for the dead. But if he was looking to the splendid reward that is laid up for those who fall asleep in godliness, it was a holy and pious thought. Therefore he made atonement for the dead, so that they might be delivered from their sin." (chapter 12, verses 44-45)
So from this time (about a century and a half before Jesus) we see the first and most enduring reason in Judaism, and then later in Christianity, to pray for the dead: We pray to ask God to forgive their sins and accept their souls into heaven.
We see this theme fully developed in Rabbinic Judaism (which calls heaven the Olam Habah, or "The World To Come," or sometimes gan eden, "The Garden of Eden"). I have said the Jewish final confession prayer with dying people: "May his/her death be an atonement for all his/her sins." In the New Testament, there are many texts urging prayers for the dead. In the Book of II Timothy (1:18) Paul prays for the deceased Onesiphorus: "May the Lord grant him to find mercy from the Lord on that day." The importance of praying for the dead not only required a belief in the soul, but also a belief that after bodily death the soul is judged by God. Catholic teaching calls this period of judgment purgatory, which is similar, though not identical, to the Jewish belief in the judgment of the soul after death.
This period of time could be up to one earthly year, which is why Jews pray for close deceased relatives (father, mother, sister, brother, son, daughter, spouse) every day for close to a year. The concept is that all our good deeds can be seen and judged during our life except for one -- and that is teaching our family to pray for our soul after we die.
Praying for the dead also developed over time into the Jewish idea of zechut avot, "The merit of the forefathers," and later the Christian belief in the Communion of Saints. This belief in all its forms in both religions is based upon the belief that our righteous ancestors or righteous saints built up such an abundance of goodness and spiritual merit in their lives that their excess virtue is available through prayer to help our dearly departed who might be just a little bit shy on the virtue scale.
So there's great merit in your praying for your husband's soul. I found this prayer on a Catholic website that might comfort you: "God our Father, Your power brings us to birth, Your providence guides our lives, and by Your command we return to dust.
"Lord, those who die still live in Your presence, their lives change but do not end.
"I pray in hope for my family, relatives and friends, and for all the dead known to You alone.
"In company with Christ, Who died and now lives, may they rejoice in Your kingdom, where all our tears are wiped away.
"Unite us together again in one family, to sing Your praise forever and ever. Amen."