What happened before those folks got in the water?
Acts 2:
14 But Peter, standing up with the eleven, raised his voice and said to them, “Men of Judea and all who dwell in Jerusalem, let this be known to you, and heed my words. 15 For these are not drunk, as you suppose, since it is only the third hour of the day. 16 But this is what was spoken by the prophet Joel:
17 ‘And it shall come to pass in the last days, says God, That I will pour out of My Spirit on all flesh; Your sons and your daughters shall prophesy, Your young men shall see visions, Your old men shall dream dreams. 18 And on My menservants and on My maidservants I will pour out My Spirit in those days; And they shall prophesy. 19 I will show wonders in heaven above And signs in the earth beneath: Blood and fire and vapor of smoke. 20 The sun shall be turned into darkness, And the moon into blood, Before the coming of the great and awesome day of the Lord. 21 And it shall come to pass That whoever calls on the name of the Lord Shall be saved.’
22 “Men of Israel, hear these words: Jesus of Nazareth, a Man attested by God to you by miracles, wonders, and signs which God did through Him in your midst, as you yourselves also know— 23 Him, being delivered by the determined purpose and foreknowledge of God, you have taken by lawless hands, have crucified, and put to death; 24 whom God raised up, having loosed the pains of death, because it was not possible that He should be held by it. 25 For David says concerning Him:
‘I foresaw the Lord always before my face, For He is at my right hand, that I may not be shaken. 26 Therefore my heart rejoiced, and my tongue was glad; Moreover my flesh also will rest in hope. 27 For You will not leave my soul in Hades, Nor will You allow Your Holy One to see corruption. 28 You have made known to me the ways of life; You will make me full of joy in Your presence.’
29 “Men and brethren, let me speak freely to you of the patriarch David, that he is both dead and buried, and his tomb is with us to this day. 30 Therefore, being a prophet, and knowing that God had sworn with an oath to him that of the fruit of his body, according to the flesh, He would raise up the Christ to sit on his throne, 31 he, foreseeing this, spoke concerning the resurrection of the Christ, that His soul was not left in Hades, nor did His flesh see corruption. 32 This Jesus God has raised up, of which we are all witnesses. 33 Therefore being exalted to the right hand of God, and having received from the Father the promise of the Holy Spirit, He poured out this which you now see and hear.
34 “For David did not ascend into the heavens, but he says himself:
‘The Lord said to my Lord, “Sit at My right hand, 35 Till I make Your enemies Your footstool.”’
36“Therefore let all the house of Israel know assuredly that God has made this Jesus, whom you crucified, both Lord and Christ.”
37 Now when they heard this, they were cut to the heart, and said to Peter and the rest of the apostles, “Men and brethren, what shall we do?”
38 Then Peter said to them, “Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit. 39 For the promise is to you and to your children, and to all who are afar off, as many as the Lord our God will call.”
40 And with many other words he testified and exhorted them, saying, “Be saved from this perverse generation.” 41 Then those who gladly received his word were baptized; and that day about three thousand souls were added to them.
Seems those who believed the Gospel Peter taught got in the water and were baptized.
Here we have Acts event 2 in chapter 3:
Acts 3:
12 And when Peter saw it, he answered unto the people, Ye men of Israel, why marvel ye at this? or why look ye so earnestly on us, as though by our own power or holiness we had made this man to walk?
13 The God of Abraham, and of Isaac, and of Jacob, the God of our fathers, hath glorified his Son Jesus; whom ye delivered up, and denied him in the presence of Pilate, when he was determined to let him go. 14 But ye denied the Holy One and the Just, and desired a murderer to be granted unto you; 15 And killed the Prince of life, whom God hath raised from the dead; whereof we are witnesses.
16 And his name through faith in his name hath made this man strong, whom ye see and know: yea, the faith which is by him hath given him this perfect soundness in the presence of you all. 17 And now, brethren, I wot that through ignorance ye did it, as did also your rulers.
18 But those things, which God before had shewed by the mouth of all his prophets, that Christ should suffer, he hath so fulfilled. 19 Repent ye therefore, and be converted, that your sins may be blotted out, when the times of refreshing shall come from the presence of the Lord. 20 And he shall send Jesus Christ, which before was preached unto you:
21 Whom the heaven must receive until the times of restitution of all things, which God hath spoken by the mouth of all his holy prophets since the world began.
22 For Moses truly said unto the fathers, A prophet shall the Lord your God raise up unto you of your brethren, like unto me; him shall ye hear in all things whatsoever he shall say unto you. 23 And it shall come to pass, that every soul, which will not hear that prophet, shall be destroyed from among the people.
24 Yea, and all the prophets from Samuel and those that follow after, as many as have spoken, have likewise foretold of these days. 25 Ye are the children of the prophets, and of the covenant which God made with our fathers, saying unto Abraham, And in thy seed shall all the kindreds of the earth be blessed.
26 Unto you first God, having raised up his Son Jesus, sent him to bless you, in turning away every one of you from his iniquities.
The crucified and risen Christ is preached by Peter in the above passage. Where is the baptism? Oh I'm sure those that did believe got in the water that day, but Peter did not preach the act of doing so as central to the Gospel. The scriptural evidence is those who trusted in the Blood of Christ for the remission of sins, the Gospel, were baptized and thus became followers of Jesus Christ. It is not an either/or. Just as previously pointed out with Cornelius. He and household heard the Gospel, believed it, those who believed it were filled with the Holy Spirit and then were baptized into the fellowship of the Way.
Now for some doctrine written by the apostle Paul. He clearly defines the Gospel and his mission from Christ:
1 Corinthians 1:
13 Is Christ divided? was Paul crucified for you? or were ye baptized in the name of Paul? 14 I thank God that I baptized none of you, but Crispus and Gaius; 15 Lest any should say that I had baptized in mine own name.
16 And I baptized also the household of Stephanas: besides, I know not whether I baptized any other. 17 For Christ sent me not to baptize, but to preach the gospel: not with wisdom of words, lest the cross of Christ should be made of none effect. 18 For the preaching of the cross is to them that perish foolishness; but unto us which are saved it is the power of God.
Now here:
1 Corinthians 15:
15 Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand; 2 By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain.
3 For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures; 4 And that he was buried, and that he rose again the third day according to the scriptures:
5 And that he was seen of Cephas, then of the twelve: 6 After that, he was seen of above five hundred brethren at once; of whom the greater part remain unto this present, but some are fallen asleep. 7 After that, he was seen of James; then of all the apostles.
8 And last of all he was seen of me also, as of one born out of due time.9 For I am the least of the apostles, that am not meet to be called an apostle, because I persecuted the church of God.
10 But by the grace of God I am what I am: and his grace which was bestowed upon me was not in vain; but I laboured more abundantly than they all: yet not I, but the grace of God which was with me.11 Therefore whether it were I or they, so we preach, and so ye believed.
The above is apostolic teaching. Which of course they were faithfully proclaiming the Gospel Jesus gave them:
Luke 24:
44 And he said unto them,These are the words which I spake unto you, while I was yet with you, that all things must be fulfilled, which were written in the law of Moses, and in the prophets, and in the psalms, concerning me. 45 Then opened he their understanding, that they might understand the scriptures,
46 And said unto them,Thus it is written, and thus it behooved Christ to suffer, and to rise from the dead the third day: 47 And that repentance and remission of sins should be preached in his name among all nations, beginning at Jerusalem. 48 And ye are witnesses of these things. 49 And, behold, I send the promise of my Father upon you: but tarry ye in the city of Jerusalem, until ye be endued with power from on high.
What is the purpose of baptism?
Why did Peter say in Acts 2 “ be baptized”?