"Seeing is believing," as the saying goes, yet Jesus says, "Blessed are they who have not seen, and yet believe." Well, the disciples who cowered behind closed doors on the evening of the first day--"for fear of the Jews"--only believed because our Lord appeared to them and showed them His hands and side. And while Thomas had insisted he would only believe if he thrusts his hand into our Lord's side, as soon as Jesus appears, he exclaims, "My Lord and my God!"
So why, then, is St. Thomas singled out as the doubting one?--It is because he did not believe the testimony of his fellow Apostles who had already beheld the risen Lord a week earlier. Well, neither has any one of us here today seen our Lord with our physical eyes--nor has anyone else since our Lord's Ascension--yet numerous saints and Holy Fathers have indeed "seen" Him with their spiritual eyes, while innumerable Christians down through the ages have experienced His presence in their lives.
So we are indeed encompassed by a "great cloud of witnesses" whose irrefutable testimonies confirm for us all the continuing and abiding presence of Christ in His Church--and in the hearts of the faithful. And so there is no excuse for those who willfully harden their hearts, refusing to acknowledge Christ as their Savior and to proclaim with St. Thomas, "My Lord and my God!"
Perhaps we have allowed our spiritual eyes to be darkened by sin; or maybe we were physically blind from birth; but neither of these circumstances (nor any power whatsoever in heaven or on earth) need separate us from the love of God in Christ Jesus. And if, indeed, the love of God abides in our hearts--even the smallest flame of this love--He shall surely reveal Himself to us according to the measure of our faith, that we too might exclaim with St. Thomas, "My Lord and my God!"