The Second Sunday in Easter is also known as Divine Mercy Sunday. The Gospel reading from St. John's Gospel recounts how our Lord mercifully revealed Himself as the Risen Lord to St. Thomas who doubted the testimony of the other apostles when they told him that they had seen Jesus who had been raised from the dead.

Readings:

Acts 2:42-47
Psalm 118:2-4, 13-15, 22-24
1 Peter 1:3-9
John 20:19-31

Here are a few commentaries on these readings:

St. Charles Borromeo Lectionary Site (PDF)

His Mercy Endures - St. Paul Center for Biblical Theology

Doubting Thomas - The Crossroads Initiative