Now Thomas, one of the twelve, called the Twin, was not with them when Jesus came.
So the other disciples told him, "We have seen the Lord." But he said to them, "Unless I see in his hands the print of the nails, and place my finger in the mark of the nails, and place my hand in his side, I will not believe."
Eight days later, his disciples were again in the house, and Thomas was with them. The doors were shut, but Jesus came and stood among them, and said, "Peace be with you."
Then he said to Thomas, "Put your finger here, and see my hands; and put out your hand, and place it in my side; do not be faithless, but believing."
Thomas answered him, "My Lord and my God!" John 20: 24-28
The Octave Day of Easter, sometimes known as Low Sunday (and also known historically as St. Thomas Sunday and Quasimodo Sunday), is the Sunday after Easter Sunday. Since 1970 Low Sunday has been officially known as the Second Sunday of Easter and on April 30, 2000, it has also been designated as Divine Mercy Sunday by Pope John Paul II.
St. Thomas Sunday? Because the Gospel reading relates the story of "Doubting Thomas," in which Thomas the Apostle comes to believe in the Resurrection of Jesus only after being told by the resurrected Christ to place his finger in the nail marks and his hand in His side. In the Gospel accounts, this event takes place on the eighth day after the Resurrection.
Divine Mercy Sunday is the culmination of the novena to the Divine Mercy of Jesus, a devotion given to St. Faustina .The devotion was actively promoted by Pope John Paul II, who officially set its commemoration on this Sunday in 2000.
Prior to the 1970 this day was called Low Sunday. It was sometimes said that the name comes from its relative unimportance compared to the solemnities of Easter Day, but I have also read that it is possible that "low" is a corruption of the Latin word Laudes, the first word of the Sequence of the day: "Laudes Salvatori voce modulemur supplici" (Let us sing praises to the Savior with humble voice).
The name Quasimodo came from the Latin text of the traditional Introit for this day, which begins "Quasi modo geniti infantes..." ("As newborn babes...", from I Peter 2:2. )