We’ve all experienced our own Exodus, our own escape from slavery, our own defeat of the armies of the enemy, our own entry into the protection and leadership of God – through baptism. And this tells us how to live as Christians.
Just so, Paul writes,
(Gal. 3:23-29 ESV) Now before faith came, we were held captive under the law, imprisoned until the coming faith would be revealed. 24 So then, the law was our guardian until Christ came, in order that we might be justified by faith. 25 But now that faith has come, we are no longer under a guardian, 26 for in Christ Jesus you are all sons of God, through faith. 27 For as many of you as were baptized into Christ have put on Christ. 28 There is neither Jew nor Greek, there is neither slave nor free, there is no male and female, for you are all one in Christ Jesus. 29 And if you are Christ’s, then you are Abraham’s offspring, heirs according to promise.
Again, we see the two great defining narratives of Judaism: sonship of Abraham and freedom from slavery. But Paul redefines these narratives in vital ways.
First, both Jews and Gentiles are Abraham’s offspring – and so inherit under God’s covenant promises given to Abraham – because we belong to Jesus (“are Christ’s” v. 29). Even Gentile converts are sons of Abraham because a son of Abraham is someone justified by faith. And we know that, like Abraham, we’re justified by faith because of our baptisms!
And there is neither slave nor free among Christians because we are all free – having been freed from sin by faith, as shown by our baptisms. There is no distinction between male and female in Christ because, unlike the male-only circumcision mark, we are marked by our baptism, received alike by male and female.
The same reframing of our stories is found in Rom 6 –
(Rom. 6:1-8 ESV) What shall we say then? Are we to continue in sin that grace may abound? 2 By no means! How can we who died to sin still live in it? 3 Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? 4 We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life. 5 For if we have been united with him in a death like his, we shall certainly be united with him in a resurrection like his.
6 We know that our old self was crucified with him in order that the body of sin might be brought to nothing, so that we would no longer be enslaved to sin. 7 For one who has died has been set free from sin. 8 Now if we have died with Christ, we believe that we will also live with him.
Again we see Paul using the language of the Exodus – freedom from slavery – in connection with baptism. Our baptisms demonstrate that we should live as Jesus-people, freed from sin and so enabled to live as were always meant to live.
Peter and Paul both argued their cases from Joel, who had long before promised a radically different new world, a kingdom in which the Spirit would be outpoured, in which everyone who calls on the name of the Lord would be saved.
(Joel 2:28-32a ESV) “And it shall come to pass afterward, that I will pour out my Spirit on all flesh; your sons and your daughters shall prophesy, your old men shall dream dreams, and your young men shall see visions. 29 Even on the male and female servants in those days I will pour out my Spirit.
30 “And I will show wonders in the heavens and on the earth, blood and fire and columns of smoke. 31 The sun shall be turned to darkness, and the moon to blood, before the great and awesome day of the LORD comes. 32 And it shall come to pass that everyone who calls on the name of the LORD shall be saved.”
Joel promised a kingdom to be marked by the outpouring of the Spirit on both male and female, slave and free, bringing in “everyone who calls on the name of the Lord,” not just Jews but Gentiles as well. Gal 3:28 is built on Joel 2:28-32! 
Peter uses Joel’s prophecy as the primary text for his sermon delivered on Pentecost in Acts 2, culminating in –
(Acts 2:38-39 ESV) And Peter said to them, “Repent and be baptized every one of you in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit. 39 For the promise is for you and for your children and for all who are far off, everyone whom the Lord our God calls to himself.”
Notice carefully. Peter quotes Joel 2:28-32a in Acts 2:17-21 as the scriptural foundation for his sermon. He says the prophecy is being fulfilled before their very eyes (v. 16). He then demonstrates from the scriptures that Jesus is not only the Messiah, but the Lord (vv. 22-26). That is, he claims that Jesus is the same “Lord” as the “LORD” on whose name we must call to be saved according to Joel 2:32a.
In Joel 2:32a, “LORD” is written in all capital letters to signify that “LORD” translates YHWH. That is, Peter is declaring that Jesus is not just the Messiah but he also YHWH – God the Son!
And then he says that to be saved, the Jews must believe in Jesus and “be baptized … in the name of Jesus Christ,” that is, that must “call on the name of the LORD” by being baptized in the name of Jesus.
Now, Peter offers no explanation at all for why baptism is the chosen means of calling on the name of the Lord, but it’s what he preached.
Parallel to Peter’s sermon in Acts 2 is the account of Paul’s conversion. After Paul was struck blind on the road to Damascus, Ananias came to him and said –
(Acts 22:14-16 ESV) And he said, “’The God of our fathers appointed you to know his will, to see the Righteous One and to hear a voice from his mouth; 15 for you will be a witness for him to everyone of what you have seen and heard. 16 And now why do you wait? Rise and be baptized and wash away your sins, calling on his name.’”
“Calling on his name” is an allusion to Joel 2:32a, and is associated with baptism, as in Acts 2:38.
Shortly thereafter, Luke records –
(Acts 9:21 ESV) And all who heard him were amazed and said, “Is not this the man who made havoc in Jerusalem of those who called upon this name? And has he not come here for this purpose, to bring them bound before the chief priests?”
By this time, “those who called upon [the name of Jesus]” has become a virtual synonym for “Christian.” “Called” is actually a present participle and would be better translated “those calling” or “those who call” as in the NIV and NET Bible. The reference is not back to a moment of baptism, but to a continual state of being. Christians continue to call on the name of the Lord, that is, they continue to rely on Jesus for forgiveness as LORD, that is, God the Son. Therefore, the phrase is not a reference to baptism but to continuous reliance on Jesus as Lord and Savior.
A key parallel passage is from Rom 9 –
(Rom. 10:9-14 ESV) because, if you confess with your mouth that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved. 10 For with the heart one believes and is justified, and with the mouth one confesses and is saved. 11 For the Scripture says, “Everyone who believes in him will not be put to shame.” 12 For there is no distinction between Jew and Greek; for the same Lord is Lord of all, bestowing his riches on all who call on him. 13 For “everyone who calls on the name of the Lord will be saved.” 14 How then will they call on him in whom they have not believed? And how are they to believe in him of whom they have never heard? And how are they to hear without someone preaching?
Notice that in v. 13, Paul, like Peter, relies on Joel 2:32a for the teaching that “everyone who calls on the name of the Lord will be saved.” However, although Paul is speaking of evangelistic preaching and how people are saved, he says nothing about baptism. Although baptism is our shared, unifying event and story, forgiveness comes by confessing “Jesus is Lord” and believing in the resurrection.
(1 Cor. 1:2 ESV) To the church of God that is in Corinth, to those sanctified in Christ Jesus, called to be saints together with all those who in every place call upon the name of our Lord Jesus Christ, both their Lord and ours:
Paul treats “those who … call upon the name of our Lord Jesus Christ” as meaning “Christians” based on Joel 2:32a.
Joel doesn’t say that “everyone who calls on the name of the Lord through baptism will be saved.” Rather, both Peter, Luke, and Paul interpret Joel as saying “everyone who calls on the name of the Lord [Jesus] will be saved.”
As a result, although Paul, Luke, and Peter treat baptism into Jesus as vitally important – as defining the narrative that defines who we are as a people – salvation is promised to all who confess Jesus as Lord. That is, the early church taught and practiced baptism as the means by which a convert first called on the name of Jesus as Lord. And this practice defined the church’s unity and how Christians should live. It was a part of the church’s shared narrative, defining them as a distinct people.
But the church did not consider baptism to be the unique, only means of calling on the name of the Lord. Rather, the promise of Joel 2:32a means what it says: “everyone who calls on the name of the LORD shall be saved.”
 See Bobby Valentine’s “Galatians 3:28, Baptism and Women in the Gathering,” Stoned-Campbell Disciple (April 22, 2016). http://stonedcampbelldisciple.com/2016/04/22/galatians-3-28-baptism-women-in-the-gathering/.
 The Churches of Christ, among many other denominations, traditionally have taught that “repent” in Acts 2:38 means “repent of all your sins.” But Peter’s sermon only accuses his audience of denying that Jesus is the Messiah and so crucifying him. These were, after all, pilgrims who’d traveled for even thousands of miles to celebrate Pentecost in Jerusalem. They were not immoral, wicked people. They were obedient Jews who denied Jesus as the Messiah. Hence, “repent” in context means to turn away from your former path of disbelief and to instead turn to Jesus in faith.
(Acts 2:36 ESV) 36 “Let all the house of Israel therefore know for certain that God has made him both Lord and Christ, this Jesus whom you crucified.”
The same is true of Acts 3:14-19, where Peter commands his hearers to repent of their lack of faith.
If this is not true, then Peter did not require his converted to believe in Jesus as a prerequisite to baptism in either of his first two gospel sermons, which is unimaginable. On the other hand, this hardly means that we don’t have to repent of our sins to be saved. After all, to have “faith” in Jesus requires that we commit to be faithful to him, as we’ve covered previously. In fact, to a Jew, believing Jesus to be Messiah and YHWH (LORD) certainly meant submitting to him as Lord, which is just another way of saying “repenting” – in fact, it’s even more exact as the goal isn’t just to give up sin but also to follow Jesus. The repentance required is both a rejection of sin and entry into God’s mission by following his Son as King/Messiah/Lord. We should preach baptism on these same terms.