St Thomas the Apostle

The mercy of God brought it to pass in wondrous manner that this doubting disciple, as he touched the bodily Wounds of his Master, should heal in us the wounds of unbelief. For the unbelief of Thomas did us more good than the faith of the disciples that believed, because, as he is brought back to faith by touching, our minds are strengthened in faith, every doubt being laid aside.

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Doubting Thomas, by Francesco Barbieri, known as “il Guercino”, ca.

For after His Resurrection, the Lord permitted that His disciple should doubt, but yet did not leave him in his doubt, just as before His birth, He willed that Mary should have a spouse, who yet did not come to her marriage bed. The disciple who doubted and touched became a true witness of the resurrection, just as the spouse of His Mother was the keeper of Her intact virginity. He touched, and cried out “My Lord and my God!” Jesus saith unto him, “Because thou hast seen Me, thou hast believed.” (St Gregory the Great, Homily 26 on the Gospels, from Matins of the feast of St Thomas the Apostle in the Breviary of St Pius V.)

Many medieval breviaries have a special O antiphon for Vespers of this feast:
O Thoma Didyme, per Christum quem meruisti tangere, te precibus rogamus altisonis, succurre nobis miseris, ne damnemur cum impiis in adventu judicis.

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The St. Thomas Altarpiece, by the Master of the St. Bartholomew Altar, 1501

O Thomas the Twin, through Christ, Whom thou didst merit to touch,with prayers resounding on high we beseech thee, come to help us in our wretchedness, lest we be damned with the wicked at the Coming of the Judge.