Who was St. Thomas the Apostle?
Almost everything we know about Thomas comes from the Gospel of John. The other Gospels list him among the Twelve and say nothing more. His name, Benedict XVI explained in a 2006 audience, comes from a Hebrew root meaning "twin," which is why John also calls him Didymus, the Greek for the same thing. Nobody knows whose twin he was.
John gives him three scenes. When Jesus decided to go back to Judea to raise Lazarus, into territory where people had tried to kill him, it was Thomas who said to the others, "Let us also go, that we may die with him" (John 11:16). Benedict calls that determination "truly exemplary." At the Last Supper, when Jesus spoke of going away, Thomas asked the question the others were too polite to ask: "Lord, we do not know where you are going; how can we know the way?" (John 14:5). It drew out one of the great answers of the New Testament: "I am the way, and the truth, and the life." Then, on Easter evening, he was not in the room. When the others told him they had seen the Lord, he said he would not believe unless he put his finger in the marks of the nails. A week later Jesus came back and offered him exactly that. Thomas answered, "My Lord and my God!" (John 20:28). Benedict XVI calls it "the most splendid profession of faith in the whole of the New Testament."
What happened afterward is tradition, and the sources are honest about how thin it is. Benedict XVI reports "an ancient tradition" that Thomas preached first in Syria and Persia, then in western India, and finally in the south of India. The Catholic Encyclopedia traces most of the detail to the Acts of Thomas, a document from about the early third century with Gnostic coloring, in which India falls to Thomas when the apostles divide the world. He is sold as a slave to an Indian king named Gundafor and in the end is killed by soldiers with spears. The Encyclopedia calls much of the story "utterly extravagant," yet it notes something odd: Gundafor matches a real king, Gondophernes, and the identification, it says, "is hardly disputed." The Encyclopedia also records the strong local tradition of Mylapore, near present-day Chennai, and discusses the Christians of the Malabar coast, though it says whether their church began with Thomas "seems difficult to determine." Franciscan Media gives the traditional date of his death as December 21, 72. The Encyclopedia finds it "difficult to discover any adequate support" for his having gone that far south, while allowing that the legend "may contain germs of truth." His reputed relics, it says, were at Edessa in the fourth century, were moved to the island of Chios in 1258, and from there to Ortona in Italy.
Why Catholics pray to St. Thomas for faith
The Church did not make Thomas the patron of doubters by decree. It made him so by reading John 20 every year in Easter week and recognizing itself. He wanted evidence. He said so in front of his friends. And Jesus did not scold him first; he came back for him.
Benedict XVI draws three lessons from the scene, and they are the reasons a Catholic in doubt goes to Thomas. First, his case "comforts us in our insecurity": the Church began with an apostle who could not believe on someone else's word. Second, doubt that is honest can end better than a vague uncertainty that never asks anything. Third, his story shows what mature faith looks like, because Jesus' last word in the scene is for us, not for him: "Blessed are those who have not seen and yet believe" (John 20:29). Benedict adds, citing Thomas Aquinas, that those who believe without seeing are the more meritorious.
There is one more thing in the scene that people in trouble notice. Jesus is identified by his wounds. Thomas does not ask for a glorious vision; he asks for the marks of the nails, and Benedict says the apostle "is not mistaken" in this, because the wounds are where Christ "reveals to us how much he loved us." Faith that has gone through loss, illness or betrayal does not usually come back by argument. It comes back the way it came back for Thomas, when Christ shows up carrying his own scars.
So a Catholic asks St. Thomas not for certainty but for his ending: to be in the room next time, and to be able to say the five words.
How to pray to St. Thomas
Pray to him any day. His feast is July 3, ranked as a feast rather than a memorial on the General Roman Calendar, and the nine days before it run June 24 to July 2. The Gospel of the feast is John 20:24-29; reading it slowly at home, aloud, is itself a prayer. His reputed relics, by the Catholic Encyclopedia's account, went from Edessa to Chios and then to Ortona on the Adriatic coast of Italy.
Say the prayer below once, then do what Thomas did: tell Jesus plainly what you cannot believe and what it would take. Go back into the room, which for a Catholic means Mass, even when faith is thin. Go to Confession and say the doubt out loud to a priest; doubt itself is not a sin, and a priest has heard it before. Read John's Gospel from chapter 11 to the end, where all three of Thomas's scenes are.
If the doubt is tied to depression, to a loss, or to anxiety that will not stop, see a doctor or a counselor as well. If you are thinking of ending your life, call emergency services or, in the United States, 988.
Thomas is remembered for the doubt. The Church keeps his feast for the sentence that followed it.