Acts 5:12-16

In the gospels, a bleeding woman approaches Jesus and touches the hem of His garment in the hope of healing. The miraculous healing that follows does not suggest a magic quality to Jesus' garment - rather the passage reveals the humble faith of the woman and the transformation that is possible in relationship to Jesus Christ. Likewise today when we hear of people looking for healing in the shadow of Peter, we should not imagine that the text describes some kind of special effect in his shadow. The point of this summary is the same point made in the gospels.
This passage falls in a section of Acts that relates the growth and growing pains of the early Church. In these verses, we have a summary which gives a quick snapshot of the common experience in those heady first days. The miracles and healing that occur here and in other passages are not actually the work of the Apostles themselves. True, their experience recalls the miracles of Jesus' own ministry - but their words and actions are powerful only because all are said and done "in the Name" of the Lord Jesus. It is His healing, reconciling power at work. However, the Lord never forces a response or healing either directly or through those whom He has sent - people must respond in humility and faith when they come into the presence of the Lord Jesus. Thus with faith, even the shadow may see the healing power of God at work. 

Psalm 118:2-4, 13-15, 22-24

This Psalm of thanksgiving appears in the readings for Easter and for the Second Sunday of Easter - the "eighth day" of the Octave of Easter.
Commentaries debate the exact life setting for this Psalm, but it is most important to notice the Christian "reread" at work in employing this text for the Easter Octave. 
The Scriptures long proclaimed that Adonai loved His people - with a faithful, enduring love. Easter rejoicing asserts that the events of the Paschal mystery are the ultimate confirmation of this faithful love. God has restored His people in the offering of His Son. 
Even the rejection of the "cornerstone" cannot stop the abundant loving mercy of God and the Lord's plan of redemption and deliverance.

Revelation 1:9-11a, 12-13, 17-19

The larger part of the Book of Revelation is composed of a lengthy vision of the author. In these verses, we touch on the beginnings of that revelation. 
We learn at the outset that the Christian community, including the author, suffer persecution for the faith. However, these events have more than earthly significance- they are the "distress" or tribulations that were associated with the end times - the Apocalypse - the final revelation of God's plan and glory at the end of time. 
The opening recalls the visions of the prophets of old who likewise visited heavenly courts and received their prophetic message from on high - recall for example the call and visions of the Prophet Ezekiel.
And the central focus of the visions is revealed here. Suffering communities, perhaps tempted to waver or despair will hear a powerful prophecy of identification and communion with the Lord Who turned loss to victory and death to life. 

John 20:19-31

This passage is rich with links to the larger Johannine narrative. Jesus' identity is being confirmed, His promises are coming to pass, and His work is being entrusted to new generations.
The Lord's greeting, "peace be with you," is on one level an ordinary greeting. In this context, however, it is so much more. In the Biblical worldview, peace is more than the absence of strife. It is the fullness of right relationship with God. The central focus of this gospel has been the truth that Jesus is the presence and glory of the Father in the world. To see and know Him is to see and know the Father. Jesus' appearance here reveals that God's plan of reconciling humanity has taken place - this is the very power of mercy, of grace, and of God's creative and restoring power. 
The gift of the Holy Spirit follows on Jesus's offering of Himself on the cross. There, He established a new family ("behold your mother...behold your son") and upon His death He gave over "the Spirit." Thus He fulfilled His promise that He would never abandon them and that He would give them and advocate Who would be His presence in His absence. 
Now in the upper room, He is not repeating the gift. In a sense He is activating it. At the cross He gave His presence, now He entrusts His work of reconciling to His disciples. Earlier, He prayed for them and consecrated them to the Father. And He promised that they would do His work and be His glory in the world. 
The memorable encounter with Thomas likewise reveals the transformation of these fragile men and women into authentic disciples with faith and the courage to proclaim that faith. All of the disciples learn here that there is not a Jesus of flesh and Galilean ministry and another Jesus Who is glorified and standing before them. The same Jesus - and a Jesus Who continues to bear the marks of His sacrifice and His fleshly humanity - stands before them now. Thomas can only exclaim in awe "My Lord and my God!" This extraordinary statement makes perfect sense to anyone who has paid attention to this Gospel. Jesus has repeatedly told us of His exalted identity - "have I not told you that I AM?"
But notice that Jesus does not merely entrust the witness and mission to this first generation. he intends that both will be passed on to future generations. And He blesses those generations, including our own, who give witness to His name and do His holy work.