The purpose for which the Lord, even Jesus Christ, came:
JOHN 10:16 And other sheep I have, which are not of this fold: them also I must bring, and they shall hear my voice; and there shall be one fold, and one shepherd.
JOHN 10:17 Therefore doth my Father love me, because I lay down my life, that I might take it again.
JOHN 10:18 No man taketh it from me, but I lay it down of myself. I have power to lay it down, and I have power to take it again. This commandment have I received of my Father.
MATTHEW 5:17 ¶ Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil.
MATTHEW 5:18 For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled.
Christ was speaking about the Law of Moses. (Because He is the fulfillment of the Law and Prophets, Jesus Christ is called the "Word"). In apparent language, John the Baptist said the following about Jesus Christ:
JOHN 1:29 ¶ The next day John seeth Jesus coming unto him, and saith, Behold the Lamb of God, which taketh away the sin of the world.
John-a prophet of God-said this even though Jesus was a man, not a lamb. Likewise, at the Passover, Jesus said the same thing:
LUKE 22:7 ¶ Then came the day of unleavened bread, when the passover must be killed.
LUKE 22:19 ¶ And he took bread, and gave thanks, and brake it, and gave unto them, saying, This is my body which is given for you: this do in remembrance of me.
Although it is true that, historically, the Passover freed the Children of Israel from bondage to Egypt, it is nevertheless a prophecy of the death of Jesus Christ. That is, Jesus Christ came to fulfill the passover, among other things (Matthew 5:17-18). Later, the apostle Paul plainly called Jesus Christ our "passover":
1 CORINTHIANS 5:7 Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ our passover is sacrificed for us:
Just as the Passover lamb was killed, so too was Jesus Christ killed (for the unblemished lamb of the Passover represents sinless Jesus Christ, such that Christ was even called "the Lamb of God").
Just as the Passover was killed to free the Children of Israel from bondage to the Egyptians, Jesus Christ was killed to free the believers from sin (for bondage to the Egyptians represents sin).
Just as the blood of the Passover was placed on the doorposts of the houses of the Children of Israel, lest God kill their firstborn, so too is the blood of Jesus Christ placed on the doorposts of the hearts of the believers, lest God kill us on the day of judgement, (for the blood of the Passover represents the blood of Jesus Christ).
Just as the Children of Israel were freed from Egypt to go to the Land of Milk and Honey, which God promised to Abraham and his seed (Genesis 13:14-15), so too have the believers been freed from their sins, so that they might go to Heaven (for the believers are counted as Abraham's seed—whether "Jew or Greek," per Galatians 3:28-29). The Land of Milk and Honey, in this story, represents Heaven.
Consider what had been taught so far. John the Baptist came to "make straight the way of the Lord:"
MARK 1:4 John did baptize in the wilderness, and preach the baptism of repentance for the remission of sins.
MARK 1:5 And there went out unto him all the land of Judaea, and they of Jerusalem, and were all baptized of him in the river of Jordan, confessing their sins.
John's baptism was for the remission of sins. Be that as it may, Jesus Christ was also baptized with John's baptism, because it was appropriate for Christ to fulfill all righteousness (cf. Matthew 3:15). Likewise, in addition to healing people and casting out devils, Jesus Christ, in general, taught:
MATTHEW 4:17 From that time Jesus began to preach, and to say, Repent: for the kingdom of heaven is at hand.
JOHN 4:1 When therefore the Lord knew how the Pharisees had heard that Jesus made and baptized more disciples than John,
In other words, Christ Himself taught at least two things: 1) He taught repentance, and 2) He taught baptism (He taught baptism at least, even though He had the power to forgive sins, while He was on the earth. See Mark 2:3-12, Matthew 9:2-8, etc.) Furthermore, He also said:
JOHN 3:3 Jesus answered and said unto him, Verily, verily, I say unto thee, Except a man be born again, he cannot see the kingdom of God.
JOHN 3:4 Nicodemus saith unto him, How can a man be born when he is old? can he enter the second time into his mother's womb, and be born?
JOHN 3:5 Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God.
In other words, Christ preached 1) Repentance (i.e., born of the spirit), and 2) Baptism (i.e., born of water). There is a distinct pattern in what was taught by both John, the prophet of God, and Jesus, the Son of God. This same pattern was continued after His resurrection.
On the third day, Christ rose from the dead. For the next forty days, He taught the disciples what to preach:
ACTS 1:2 Until the day in which he was taken up, after that he through the Holy Ghost had given commandments unto the apostles whom he had chosen:
ACTS 1:3 To whom also he shewed himself alive after his passion by many infallible proofs, being seen of them forty days, and speaking of the things pertaining to the kingdom of God:
Some of the events of these forty days are also recorded at the end of Matthew, Mark, Luke, and John, in addition to the beginning of Acts.
Let us now examine some of the things that "pertain to the kingdom of God" (Acts 1:3) that the Lord Jesus Christ taught during this forty day interval.
LUKE 24:45 Then opened he their understanding, that they might understand the scriptures,
LUKE 24:46 And said unto them, Thus it is written, and thus it behoved Christ to suffer, and to rise from the dead the third day:
LUKE 24:47 And that repentance and remission of sins should be preached in his name among all nations, beginning at Jerusalem.
Here, He said it plainly: He told them to preach 1) Repentance, and 2) Remission of sins. It should be noted that here, that at Luke 24:46-47, that He said to preach these things in the name of [Jesus] Christ.
Matthew records part of another conversation during the same forty day period:
MATTHEW 28:18 And Jesus came and spake unto them, saying, All power is given unto me in heaven and in earth.
MATTHEW 28:19 Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:
MATTHEW 28:20 Teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you alway, even unto the end of the world. Amen.
In other words, at verse 19 He taught: 2) Remission of sins (i.e., baptism), and from verse 20: He taught 1) Repentance. These are the same two items, but in reversed order. At Luke 24:46-47, He said that these things were to be preached in "his name" (that is, in "Christ's" name), but at Matthew 28:19, that this was to be done "in the name of the Father, and of the Son, and of the Holy Ghost." There is no contradiction here, since the name of the Father, and of the Son, and of the Holy Ghost, as given among men is Jesus Christ. Beginning at Acts 2:38, the apostles did these things in the name of Jesus Christ, per His instructions.
Likewise, Mark records part of yet another conversation after His resurrection:
MARK 16:15 And he said unto them, Go ye into all the world, and preach the gospel to every creature.
MARK 16:16 He that believeth and is baptized shall be saved; but he that believeth not shall be damned.
In Mark 16:16, the same two elements are present: 1) repentance ("he that believeth...") and 2) remission of sins ("...and is baptized"). Note that in Mark 16:16, the Lord Jesus Christ explicitly made baptism a requirement for salvation!
In each case He is speaking about baptism in water, not baptism of the Holy Ghost. No man has the power to baptize with the Holy Ghost (only God can do that). It should therefore be obvious that He commanded them to baptize in water at Matthew 28:19. This is a simple deduction, really, for baptism in the Holy Ghost is a "promise" and a "gift" (cf. Acts 2:38-39), and John the Baptist identified Jesus Christ as the one who would baptize with the Holy Ghost:
MARK 1:8 I indeed have baptized you with water: but he shall baptize you with the Holy Ghost.