Upon reaching Acts 2:14, it’s time for Peter to explain what is taking place and in doing so, we witness the first sermon of the church age as he explains what has happened on this particular day of Pentecost straight from the OT Scriptures.  More specifically, he will highlight that the sending of the Holy Spirit demonstrates saving power.  Yes, Christ has purchased salvation for God’s people with his own blood, but the Holy Spirit’s work is required to apply that salvation to a sinner to the end that the sinner calls upon the Lord to be saved. 

So rather than being astonished or disenchanted by the tongues speaking, Peter wants this crowd in Acts 2 to know that salvation has come upon them—either repent and turn to the Lord Jesus Christ OR perish in the judgment of the Day of the Lord.  There is a similar dividing line for all who are confronted with the gospel—either we already have called upon the Lord for salvation due to the saving work of the Holy Spirit in our hearts OR we have not.  If you have received this salvation, then your study of passages about salvation should solidify the hope you have in God’s saving work, since the Father planned it, the Son accomplished it and the Spirit applied it.  If you have not received this salvation due to never turning from trusting in yourself, while casting all your hope on Jesus Christ’s finished work for the forgiveness of your sins and a complete righteousness granted to you by faith alone, then this will be a very appropriate time to call upon the Lord to be saved from the hopelessness and damning nature of your sin.  In the book of Romans, the Apostle Paul teaches that the wages of sin is death, but he also teaches at the beginning of 2 Cor. 6, while quoting the prophet Isaiah—Behold, now is “the acceptable time,” behold, now is “the day of salvation.   

That is true because we live in the age of the Holy Spirit’s New Covenant ministry and it is this ministry that began in Acts 2.