The key element in understanding Scripture is to rightly divide it. (11 Tim. 2:15) It is imperative to determine who the Word is being addressed to. For example when God dealt with Noah He instructed Noah to build an ark. We do not read this passage today and determine, well God’s will is for us to build an ark and then build one. Of course we do not. God was instructing Noah to do what was necessary at the time for his salvation. Moses and the children of Israel had to keep a multitude of laws and sacrifices but again, this was for a particular people for a particular time. So we see how the message from God if not rightly divided and rightly applied can create confusion. The misapplication of certain passages can cause the rise of improper doctrine even to the point of heresies.
Let us look at the passage in Acts chapter 2. Peter is not speaking to us today and the message has no application to receiving salvation in this dispensation. The Gospel of the Grace of God was given to the Apostle Paul who at the time of this sermon was still a Pharisee.
If you were to use this passage for your salvation then you must be baptized in order to receive salvation. According to the New Testament Pauline epistle we know this is not true for the born again believer.( Acts 2:38) Water baptism for us just makes us wet and has no saving grace.

Acts 2:14] But Peter, standing up with the eleven, lifted up his voice, and said unto them, Ye men of Judaea, and all ye that dwell at Jerusalem, be this known unto you, and hearken to my words:
[15] For these are not drunken, as ye suppose, seeing it is but the third hour of the day.
[16] But this is that which was spoken by the prophet Joel;
[17] And it shall come to pass in the last days, saith God,I will pour out of my Spirit upon all flesh: and your sons and your daughters shall prophesy, and your young men shall see visions, and your old men shall dream dreams:
[18] And on my servants and on my handmaidens I will pour out in those days of my Spirit; and they shall prophesy:
[19] And I will shew wonders in heaven above, and signs in the earth beneath; blood, and fire, and vapour of smoke:
[20] The sun shall be turned into darkness, and the moon into blood, before that great and notable day of the Lord come:
[21] And it shall come to pass, that whosoever shall call on the name of the Lord shall be saved.

Peter begins his message with a quotation from Joel 2:28-32. Those in his Jewish audience, being familiar with the Old Testament prophets, would have understood the statements in Joel come after the promise the Lord God would be in the midst of Israel just before the pouring out. Peter was telling them Jesus, the Lord God, had been in their midst. NOTE verse 22 of our passage:

[22] Ye men of Israel, hear these words; Jesus of Nazareth, a man approved of God among you by miracles and wonders and signs, which God did by him in the midst of you, as ye yourselves also know:

Please note to whom Peter is speaking. The passage clearly states : the men of Israel ! Are you, the lost Gentile, a man of Israel? Then the Holy Spirit must not be talking to you in this passage.
Whether Peter actually believed the events were a direct fulfillment of the prophecy or was attempting to prove a point we do not know. If he thought this was a direct fulfillment of the prophecy we know him to be wrong. The Holy Spirit was NOT pour out on ALL flesh, the sun did NOT darken, the moon did NOT turn to blood, the notable day of the Lord did NOT happen. The wonders Jesus performed did NOT involve smoke, vapor, fire or blood. The only statement which could be said to be accurate is the saving of those who call upon the Lord, which by the way is quoted in Romans by the Apostle Paul as being current for this dispensation. (Romans 10:13). I believe Peter did indeed think this scripture was being fulfilled as the restoration of Israel as an independent nation ruling the world was foremost on the Apostles mind (see Acts 1:6) and was expecting Christ to come right back and destroy the Roman army and restore the kingdom.
Peter believing this is now expecting the entirety of the passage to be fulfilled.

[23] Him, being delivered by the determinate counsel and foreknowledge of God, ye have taken, and by wicked hands have crucified and slain:
[24] Whom God hath raised up, having loosed the pains of death: because it was not possible that he should be holden of it.
[25] For David speaketh concerning him, I foresaw the Lord always before my face, for he is on my right hand, that I should not be moved:
[26] Therefore did my heart rejoice, and my tongue was glad; moreover also my flesh shall rest in hope:
[27] Because thou wilt not leave my soul in hell, neither wilt thou suffer thine Holy One to see corruption.
[28] Thou hast made known to me the ways of life; thou shalt make me full of joy with thy countenance.
[29] Men and brethren, let me freely speak unto you of the patriarch David, that he is both dead and buried, and his sepulchre is with us unto this day.
[30] Therefore being a prophet, and knowing that God had sworn with an oath to him, that of the fruit of his loins, according to the flesh, he would raise up Christ to sit on his throne;
[31] He seeing this before spake of the resurrection of Christ, that his soul was not left in hell, neither his flesh did see corruption.
[32] This Jesus hath God raised up, whereof we all are witnesses.
[33] Therefore being by the right hand of God exalted, and having received of the Father the promise of the Holy Ghost, he hath shed forth this, which ye now see and hear.
[34] For David is not ascended into the heavens: but he saith himself, The LORD said unto my Lord, Sit thou on my right hand,
[35] Until I make thy foes thy footstool.
[36] Therefore let all the house of Israel know assuredly, that God hath made that same Jesus, whom ye have crucified, both Lord and Christ.

Peter does not preach a substitution death of Jesus nor the shedding of His blood being an atonement for sin but rather they wickedly killed Him (though it was within God’s plan). He preached Christ went to Hell but God raised Him up and exalted Him to His right hand where He is waiting for His enemies to be destroyed.
He preached Christ is going to sit on the throne of David. So this Jewish audience understood in light of the Old Testament Christ was coming back to rule and the expectation was one of immediacy. They out of fear for a retribution by Jesus cried out what must they do. Not a fear of condemnation to hell or eternity in the lake of fire but rather one of fear of retribution for killing Jesus. Look at the message! No mention of dying in your sins, blood shedding atonement, eternal life, being born again, forgiveness of ALL sins, nothing associated with the saving of a soul. This is NOT the gospel as we know it.

[37] Now when they heard this, they were pricked in their heart, and said unto Peter and to the rest of the apostles, Men and brethren, what shall we do?
[38] Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.
[39] For the promise is unto you, and to your children, and to all that are afar off, even as many as the Lord our God shall call.
[40] And with many other words did he testify and exhort, saying, Save yourselves from this untoward generation.

Repent and baptism for the remission of what sins? Verse 23 in his message, “ye have taken” and slain Jesus. The murder of Jesus.  What promise would they receive? Forgiveness for the killing of Jesus and the Holy Spirit. The only other promises the Jews knew of would be the restoration of the kingdom. Remember the message which had been preached by John the Baptist, Jesus and the Apostles ? REPENT FOR THE KINGDOM IS AT HAND. The message has not changed yet to the substitution death of Christ and eternal life promised to believers. Being born again is not even in their minds. They are NOT being taught salvation from Hell but rather, the “untoward generation”, the one who killed Jesus. (vs. 40)

[41] Then they that gladly received his word were baptized: and the same day there were added unto them about three thousand souls.

If you believe this had anything to do with our gospel then indeed you must sell all that you have and join a communal church. (Acts 2:44-47) After all, they had no need of possessions because they were anticipating the imminent return of Jesus to sit on His throne in Jerusalem and the destruction of those who had destroyed Him.