In Acts 2, when is seeking to explain what has happened, he quotes from the prophet Joel:
‘In the last days,’ God says,Acts 2:17-21
‘I will pour out my Spirit upon all people.
Your sons and daughters will prophesy.
Your young men will see visions,
and your old men will dream dreams.
18 In those days I will pour out my Spirit
even on my servants—men and women alike—
and they will prophesy.
19 And I will cause wonders in the heavens above
and signs on the earth below—
blood and fire and clouds of smoke.
20 The sun will become dark,
and the moon will turn blood red
before that great and glorious day of the Lord arrives.
21 But everyone who calls on the name of the Lord
will be saved.
Joel 2 promises that God will restore his people, he will defeat their enemies and remove their afflictions including famine and pestilence. It’s in that context that God will pour out his Spirit.
So, observe two things here. First of all, the Joel reference is telling us that Jesus’ death and resurrection has defeated the enemy of God’s people and lifted the curse upon them. Of course, the enemy is greater and the curse worse than the immediate circumstances of Joel’s day. The enemy is Satan & sin. The curse is the penalty of death.
Secondly, I think we can see why there is a particular focus on prophecy and visions. A people under judgement and curse are a people exiled from God’s presence. They are a people living in silence because if they do not know God’s loving presence then nor do they hear him speak or see him act.
Joel and therefore Peter are saying that God is stepping in close again and gathering his people to himself. He’s opening their blind eyes to see him and taking away their deafness so that they can hear him. That is therefore marked by dreams, visions and prophecy. A seeing and hearing people live get to know a living, speaking and acting God.