In the Orthodox Tradition, the Sunday after Pascha bears two titles: Antipascha and St. Thomas Sunday. The first refers to the theological meaning of Sunday itself; the second refers to the historical events having taken place one week after our Lord's Resurrection.
Antipascha is a Greek word meaning "instead of Pascha." As St. John Chrysostom points out, "It is always Pascha" (Homily 5, "On First Timothy"); that is, every Sunday Divine Liturgy has the same power, grace, and gifts as the Feast of Pascha itself. Therefore the Sunday (and every Sunday) after the Feast of feasts has the same place within Orthodox faith and practice as Pascha – it is Antipascha.
Pascha is the feast of our Lord's Resurrection from the dead which occurred on the first day of the week, which we call Sunday. Though Divine Liturgy with Holy Communion can be served any day of the week, and often is, the Orthodox invariably serve Divine Liturgy on Sunday, the Day of Resurrection. "Even if all of the other days of the week belong to the Lord, being His creations, none of them, however, bear His Name, for only that one and eighth day was worthy to be named the Lord's Day (Gk., Kyriake) after the Lord (see 1 Cor. 16:2 & Rev. 1:10). First, because on Sunday, and no other day, the Lord's resurrection occurred. Second, because that day, apart from all of the other days is especially consecrated to the Lord" (St. Nicodemus the Hagiorite, "Concerning the Prerogatives of Sunday"). Russian is more explicit: the first day of the week (Sunday) is called Voskresenie (lit., Resurrection-day).
As important as the Feast of Pascha is and has become in Orthodox popular practice, Antipascha reiterates the essential fact that each and every Sunday Divine Liturgy is just as important in God’s plan of salvation for His people. Christ's Resurrection communicated to the baptized faithful in His very Body and Blood is the defining reality of the Christian Church with its members, the truth for which we are always preparing to receive worthily and from which we are always striving to live worthily.
To this end the Risen Christ reappeared to His disciples "after eight days," this time the apostle Thomas, called the Twin, being with the others (John 20:19-31). The previous Sunday, the very day of our Lord's Resurrection, Jesus appeared to His disciples where they were assembled behind shut doors "for fear of the Jews," and Thomas was not with them. Later hearing of Christ's appearance, Thomas expressed his disbelief in the Resurrection "unless I see in His hands the print of the nails." So Christ came to His disciples again and said to Thomas: "Reach your finger here, and look at My hands; and reach your hand here, and put it into My side. Do not be unbelieving, but believing"; to which Thomas answered, "My Lord and my God!"
"O most wonderful doubt of Thomas! It brought the hearts of the faithful to knowledge… Glory to Thee, O Lord, for Thou didst confirm Thomas in faith, and hast trampled death by death!" (Lord, I Call verses). Thomas wasn't the only apostle to doubt the resurrection of Christ Jesus. They all did not at first believe (cf. Matt. 28:17; Mk. 16:14; Lk. 24:11). So the Lord Jesus provided "infallible proofs" (Acts 1:3; see 1 Cor. 15:5-8) that He was alive. This episode with Thomas happened by dispensation from God to overcome his unbelief and to provide assurance to the succeeding generations of those who would believe in the crucified and risen Savior.
"Jesus said to him, 'Thomas, because you have seen Me, you have believed. Blessed are those who have not seen and yet have believed'…these [signs] are written that you may believe that Jesus is the Christ, the Son of God, and that believing you may have life in His name"(John 20:29, 31). "Blessed be the God and Father of our Lord Jesus Christ, who according to His abundant mercy has begotten us again to a living hope through the resurrection of Jesus Christ from the dead… whom having not seen you love. Though now you do not see Him, yet believing, you rejoice with joy inexpressible and full of glory" (1 Pet. 1:3, 8).
This Thomas Sunday, the Sunday after Pascha – Antipascha – we contend with those same doubts of the resurrection. Once again the Risen Christ condescends to our weaknesses and insecurities to break the bars of unbelief with His very Presence in our midst, His Body and Blood in the Liturgy for our forgiveness and incorruptible life.