Baptism of Repentance
The ministry of the kingdom did not begin with the earthly ministry of Jesus but rather began with the baptism of John the Baptist.

Acts.1:16-26
[22] Beginning from the baptism of John, unto that same day that he was taken up from us, must one be ordained to be a witness with us of his resurrection.

The Baptism of John was preparatory. He was in the process of preparing a Jewish body to receive their Jewish King. In order for Israel to receive her King they must need repent. (Just as in the days of Tribulation the nation of Israel will have the two witnesses preaching the gospel of the kingdom which was to REPENT and Receive your King.) They were not prepared to receive Him as a dying Savior but as a ruler on a throne and delivered from their physical enemies. The baptism was done for the cleansing away of their sins.

Mic.7:[19] He will turn again, he will have compassion upon us; he will subdue our iniquities; and thou wilt cast all their sins into the depths of the sea.

Pss.51:[2] Wash me throughly from mine iniquity, and cleanse me from my sin.

The baptism showing they had repented and placed their faith in the forgiveness of God.
That they were expecting salvation from their physical enemies is evident in the prophecy of Zacharias:

Luke.1:[67] And his father Zacharias was filled with the Holy Ghost, and prophesied, saying,
[68] Blessed be the Lord God of Israel; for he hath visited and redeemed his people,
[69] And hath raised up an horn of salvation for us in the house of his servant David;
[70] As he spake by the mouth of his holy prophets, which have been since the world began:
[71] That we should be saved from our enemies, and from the hand of all that hate us;
[72] To perform the mercy promised to our fathers, and to remember his holy covenant;
[73] The oath which he sware to our father Abraham,
[74] That he would grant unto us, that we being delivered out of the hand of our enemies might serve him without fear,
[75] In holiness and righteousness before him, all the days of our life.
[76] And thou, child, shalt be called the prophet of the Highest: for thou shalt go before the face of the Lord to prepare his ways;
[77] To give knowledge of salvation unto his people by the remission of their sins,
[78] Through the tender mercy of our God; whereby the dayspring from on high hath visited us,
[79] To give light to them that sit in darkness and in the shadow of death, to guide our feet into the way of peace.
[80] And the child grew, and waxed strong in spirit, and was in the deserts till the day of his shewing unto Israel.

John the Baptist was the forerunner of the KING of Israel. His baptism was NOT the symbolic baptism which is practiced by the church today as a sign of faith in the death, burial and resurrection of Jesus Christ as Lord and Savior but one of necessity as proof of repentance from one’s sins and the preparing of the person for the reception of the King.

Matt.3:[1] In those days came John the Baptist, preaching in the wilderness of Judaea,
[2] And saying, Repent ye: for the kingdom of heaven is at hand.
[3] For this is he that was spoken of by the prophet Esaias, saying, The voice of one crying in the wilderness, Prepare ye the way of the Lord, make his paths straight.
[4] And the same John had his raiment of camel’s hair, and a leathern girdle about his loins; and his meat was locusts and wild honey.
[5] Then went out to him Jerusalem, and all Judaea, and all the region round about Jordan,
[6] And were baptized of him in Jordan, confessing their sins.
[7] But when he saw many of the Pharisees and Sadducees come to his baptism, he said unto them, O generation of vipers, who hath warned you to flee from the wrath to come?
[8] Bring forth therefore fruits meet for repentance:
[9] And think not to say within yourselves, We have Abraham to our father: for I say unto you, that God is able of these stones to raise up children unto Abraham.
[10] And now also the axe is laid unto the root of the trees: therefore every tree which bringeth not forth good fruit is hewn down, and cast into the fire.
[11] I indeed baptize you with water unto repentance: but he that cometh after me is mightier than I, whose shoes I am not worthy to bear: he shall baptize you with the Holy Ghost, and with fire:
[12] Whose fan is in his hand, and he will throughly purge his floor, and gather his wheat into the garner; but he will burn up the chaff with unquenchable fire.

Luke.3:[1] Now in the fifteenth year of the reign of Tiberius Caesar, Pontius Pilate being governor of Judaea, and Herod being tetrarch of Galilee, and his brother Philip tetrarch of Ituraea and of the region of Trachonitis, and Lysanias the tetrarch of Abilene,
[2] Annas and Caiaphas being the high priests, the word of God came unto John the son of Zacharias in the wilderness.
[3] And he came into all the country about Jordan, preaching the baptism of repentance for the remission of sins;
[4] As it is written in the book of the words of Esaias the prophet, saying, The voice of one crying in the wilderness, Prepare ye the way of the Lord, make his paths straight.
[5] Every valley shall be filled, and every mountain and hill shall be brought low; and the crooked shall be made straight, and the rough ways shall be made smooth;
[6] And all flesh shall see the salvation of God.
[7] Then said he to the multitude that came forth to be baptized of him, O generation of vipers, who hath warned you to flee from the wrath to come?
[8] Bring forth therefore fruits worthy of repentance, and begin not to say within yourselves, We have Abraham to our father: for I say unto you, That God is able of these stones to raise up children unto Abraham.
[9] And now also the axe is laid unto the root of the trees: every tree therefore which bringeth not forth good fruit is hewn down, and cast into the fire.
[10] And the people asked him, saying, What shall we do then?
[11] He answereth and saith unto them, He that hath two coats, let him impart to him that hath none; and he that hath meat, let him do likewise.
[12] Then came also publicans to be baptized, and said unto him, Master, what shall we do?
[13] And he said unto them, Exact no more than that which is appointed you.
[14] And the soldiers likewise demanded of him, saying, And what shall we do? And he said unto them, Do violence to no man, neither accuse any falsely; and be content with your wages.

The baptism was to be followed after by works on the part of receivers showing they had indeed repented of their evil deeds.

Luke 7:[26] But what went ye out for to see? A prophet? Yea, I say unto you, and much more than a prophet.
[27] This is he, of whom it is written, Behold, I send my messenger before thy face, which shall prepare thy way before thee.
[28] For I say unto you, Among those that are born of women there is not a greater prophet than John the Baptist: but he that is least in the kingdom of God is greater than he.
[29] And all the people that heard him, and the publicans, justified God, being baptized with the baptism of John.
[30] But the Pharisees and lawyers rejected the counsel of God against themselves, being not baptized of him..

Those who repented and received the baptism of John, God gave to the Son for a possession.

In Matthew chapter 14 verse 12 we find after the death of John the Baptist his disciples came to Jesus. This action was the beginning of the end of the offering of the kingdom at that time to the nation of Israel. Jesus said the law and prophets prophesied until the coming of John the Baptist and the kingdom now suffered violence. Which indeed was done with the imprisoning and death of John and culminating in the Crucifixion of our Lord.

The baptism offered by Peter was post-Resurrection BUT PRE-GOSPEL of Grace. It was preached to Israel as a nation and involved the repentance of MURDERING Jesus. None of the church epistles or Christian doctrine existed at this time. It was a period of flux between the kingdom gospel of the offering to Israel (Acts 2:22) and the gospel of grace given after the calling of the Apostle Paul.
Note in Peter’s message the end time connotation and the second advent being expected at that time. (Acts 2:19-22)

So it is no shock to see the message of baptismal regeneration being taught to the NATION of Israel for a means of preparing for their EARTHLY KINGDOM.
Acts 2:36-39

We must keep in our minds with great clarity the message of Acts 2 is for the nation of Israel and no matter how hard you examine the message you will not find salvation by grace through faith in the passage at any point. (Verse 22)
It is under the Baptism of Repentance which John began that the early church pre-Pauline doctrine operated. As the kingdom was still in sight for Israel. The offer of the kingdom continued through the deacon Steven whom the Jews also rejected and killed.
Even with the choosing of a replacement for Judas it was determined to have begun NOT with the Crucifixion but with the BAPTISM OF JOHN.

Acts.1:16-26
[22] Beginning from the baptism of John, unto that same day that he was taken up from us, must one be ordained to be a witness with us of his resurrection.

It was not until Acts chapter 10 when God showed Peter that the door was open to the Gentiles.
Acts.10:[36] The word which God sent unto the children of Israel, preaching peace by Jesus Christ: (he is Lord of all:)
[37] That word, I say, ye know, which was published throughout all Judaea, and began from Galilee, after the baptism which John preached;

Again, Peter’s beginning point for his understanding of the ministry did NOT begin with the Crucifixion nor the Resurrection but with the baptism of John. It was not the baptism of Jesus by John BUT the baptism John preached which was Repent for the KINGDOM of God is at hand and baptismal regeneration.
Peter did not seem sure of the ministry to Gentiles but the Holy Spirit exhibited the will of God. (Acts 10:44-45)

Yet still the gospel of the grace given to Paul directly from Jesus had not been given and the operation was still moving forward based upon a baptism of repentance.

The persecution continued in Acts chapter twelve the Apostle James was put to death by Herod and Peter imprisoned and in Acts chapter 13 we see the calling out of Saul (Paul) and Barnabas to be sent to the Gentiles. But it is noteworthy that these also went to the Jews FIRST (Acts 13:5). The Jewish rejection not being fully complete until offered on three known continents. (Asia, Africa and Europe)
The gospel of grace being first preached in Acts 13:38-39.

As late as Acts 18 and 19 there were still those who only preached the baptism of repentance of John.
That it was different than what we do now is evident by the necessity to teach them the full truth of the gospel and proper baptism. Even to this day we find those who would teach the church baptismal regeneration. We also find those who attempt to put the church under the law. We find those who attempt to teach the church from the Jewish Epistles from the Apostles to the Jews. There is no substitute for the teaching of the Word of God rightly divided. Most, if not all, of the confusing doctrine and supposed contradiction of scripture comes from the putting together the things which must be divided.