The Outpouring of the Holy Spirit Prophesied
Acts 2:14 says, "But Peter, standing with the eleven, lifted up his voice and addressed them: 'Men of Judea and all who dwell in Jerusalem, let this be known to you, and give ear to my words.'"
Verse 22 says, "Men of Israel, hear these words."
Peter was speaking to thousands of people. Yet, who are the ones responsible to listen? The audience. No matter how flashy or dull the speaker might be, people have a responsibility to listen carefully.
In Luke 8:18, Jesus said, "Take care then how you hear."
If Jesus, the most gifted preacher of all time, told His audience they were responsible to listen, we should take it seriously as well. We should listen carefully when God's Word is proclaimed.
Before the speaker even stands up to preach, we should pray, "God, give me ears to hear your message this morning. What do you want me to learn today? Speak to me through your Word. Amen"
Many times what listeners take away from a message was not the main point the preacher was trying to make but something the Holy Spirit lay on the heart of the listener.
This is how Peter began his message in Acts 2:14: "But Peter, standing with the eleven, lifted up his voice and addressed them: 'Men of Judea and all who dwell in Jerusalem, let this be known to you, and give ear to my words. For these people are not drunk, as you suppose, since it is only the third hour of the day.'"
He didn't ignore the crowd's accusation nor did he become defensive, he simply pointed out it wasn't even noon yet. Of course, they weren't drunk.
The same hostile crowd who had called for Jesus's crucifixion was now mocking the disciples. But what happened? The Holy Spirit worked through Peter to break the ice. He disarmed the critics long enough to grab the attention of the audience and they heard his message.
As Peter quotes from Joel, he makes three points.
First, God sends the Holy Spirit on all flesh. "And in the last days it shall be, God declares, that I will pour out my Spirit on all flesh, and your sons and your daughters shall prophesy, and your young men shall see visions, and your old men shall dream dreams" (v. 17).
Under the Old Covenant, certain people were filled with the Spirit at certain times for specific purposes. Now, under the New Covenant, the outpouring of the Holy Spirit is for all who call upon the name of the Lord. (See 1 Corinthians 12:13.) There is no believer today who lacks the presence of the Holy Spirit dwelling within them.
Second, because the Spirit has come, there will come a time of judgment. "And I will show wonders in the heavens above and signs on the earth below, blood, and fire, and vapor of smoke; the sun shall be turned to darkness and the moon to blood, before the day of the Lord comes, the great and magnificent day" (v. 19).
The imagery Peter uses comes from the great thunderstorms of Palestine. There is a lurid blood-red hue of clouds in the sky with the clouds rolling like boiling pillars in the sky. It symbolizes both bloodshed and fire. 
The coming judgment could begin today, tomorrow, or 3000 years from now. But it's coming and we know it's coming because the prophecy of the coming of the Spirit was fulfilled at Pentecost.
The point Peter was making was the, because the Holy Spirit had come, the Messianic age had begun and horrible judgment would follow.
Still, Joel offered good news. Verse 21 says, "Everyone who calls upon the name of the Lord shall be saved."
God provided a way for escape, not only to a certain nation but to anyone who would call on the name of the Lord. Even though it would be several years after Joel's prophecy until the gospel would be proclaimed to Gentiles, the prophet made this wondrous proclamation.
Many in the crowd were likely shocked when Peter told them the Lord who would save was the risen Savior, Jesus Christ.
Jesus Authenticated as Lord
Peter showed how God authenticated Jesus through His miracles. "Men of Israel, hear these words: Jesus of Nazareth, a man attested to you by God with mighty works and wonders and signs that God did through him in your midst, as you yourselves know" (Acts 2:22).
Many in the knew of Jesus's life and miraculous works. Even Jesus's enemies had to admit He did miracles. These miracles authenticated Jesus as Lord.
Peter showed Jesus as Lord by referring to His death. "This Jesus, delivered up according to the definite plan and foreknowledge of God, you crucified and killed by the hands of lawless men" (v. 23).
The religious leaders didn't believe Jesus was God in the flesh. They considered this to be blasphemy. They wanted Him dead.
Everyone assumed death invalided His claim to be Lord. But what did Peter say? Jesus wasn't killed because He was a victim of His enemies. He was killed because God predestined it before the foundations of the world. Before the universe was spoken into existence, God predestined Jesus to die on the cross to save His people. Jesus's death on the cross didn't invalidate Him as Lord. It fulfilled God's eternal decree.
Although the God predestined Jesus to suffer and die, this doesn't nullify free will. Instead, God uses everything to accomplish His eternal purpose, even the evil acts of sinful men and women.
Peter also showed Jesus to be Lord by declaring His resurrection.
There is nothing man can do to thwart God's plan. God predestined, man carried out, and God raised Him Jesus from the dead.
Jesus' miracles, death and resurrection all authenticate Him as Lord. But there is one final piece of evidence Peter proclaimed, Jesus's ascension. Peter quoted Psalm 110:1, "The Lord says to my Lord: 'Sit at my right hand, until I make your enemies your footstool.'"
They all knew King David was buried in Jerusalem. His body had decayed. Yet Jesus, who died and rose from the grave, ascended to the Father and is now seated at God's right hand. Peter was clear here that Jesus Christ is the true Messiah.
Peter Leads the Crowd's Response
Verse 37, "Now when they heard this they were cut to the heart, and said to Peter and the rest of the apostles, 'Brothers, what shall we do?'"
They were "cut to the heart." The previously antagonistic crowd now referred the apostles as brothers.
In John 16:8 Jesus had said, "And when he [the Holy Spirit] comes, he will convict the world concerning sin and righteousness and judgment."
As Ezekiel prophesied, "And I will give you a new heart, and a new spirit I will put within you. And I will remove the heart of stone ... and give you a heart of flesh" (Ezekiel 36:26).
And what did Peter tell them to do? He instructed them first to repent, to turn from their sin.
In Howard Marshall's commentary on Acts, he said this about repentance:
"The word indicates a change of direction in a person's life rather than simply a mental change of attitude or a feeling of remorse; it signifies a turning away from a sinful and godless way of life. In one sense this is something of which man is incapable by himself, and therefore, although men can be commanded to repent, it can also be said that repentance is a gift from God (5:31; 11:18; 2 Tim. 2:25). To turn away from our flesh, turn away from the old man, turn away from sin and death and turn to Christ is not something we can do on our own. The only way anyone can truly repent, is if the Holy Spirit gives us the gift of repentance for us to repent. The only way anyone can have faith in the Lord Jesus Christ is to repent." 
The second thing Peter told the crowd to do was to be baptized. Each new believer had to respond individually. Salvation is always a personal transaction between and individual and God. We are to make a public confession of our faith and commitment to Christ.
Although some disagree, baptism isn't a means to salvation. Instead, it's evidence that we have been saved. Consider the believing thief on the cross. Jesus assured him he would be in Paradise that very day—without any means of being baptized.
Acts 2:40 says, "And with many other words he bore witness and continued to exhort them, saying, 'Save yourselves from this crooked generation.'"
What was the result of Peter's sermon and invitation to be saved? Verse 41 says, "So those who received his word were baptized, and there were added that day about three thousand souls."
It's amazing to see how God used Peter here. So much of modern evangelism has it wrong. We are not to talk about sin or investing in other people's lives. We are not to tell listeners they must break away from their sinful culture. But Peter called the crowd to repent of their sin and be baptized, to profess Christ and turn from the culture.
Biblical evangelism is not about making people feel good about who they are or that God loves them just as they are.
Jeremiah 17:9 says, "The heart is deceitful above all things, and desperately sick."
The world elevates flesh; the Bible says to kill the flesh. Biblical evangelism isn't about making people feel good about their sin. It's about showing them who Christ truly is, the Lord of the universe, the One who offered Himself up for our sins and was raised from the dead. Because of our sin, we were in danger of God's divine judgment. So, Christ willing died on the cross as payment for our sin. We must call out to Him and ask Him to forgive our sins. We must trust in His work on the cross and that His resurrection conquered sin and dead. To this day, He saves those who do so.
 Ellicott's Commentary for English Readers
 The Acts of the Apostles: An Introduction and Commentary. Pg 80