Baptism in Water is not an optional extra in the Bible.  It is the necessary second step after first surrendering to Jesus and asking Him to come and live in us.   Baptism is important because going under the waters is symbolic of dying to self and our old way of selfish living (Biblically, self is not our identity or soul - self is the essence of selfishness in us that desires our way instead of God's way).  Being raised up out of the water is symbolic of being made fully alive in Jesus' Resurrection Life.  His Life is a gift resident inside us that we can and must live from in order to be able to naturally be in harmony with Him, want to obey His commands and live in the ways of His Kingdom.

Full release of resurrection Life is not ours until we are baptised in water, and we are sealed into His life as a result of this prophetic act of obedience.   There are some parables to be seen in the Biblical way of doing this.   One of these is others baptising us. This is a parable of needing to rely on God for Life which produces self control, and also that salvation is not something we can do for ourselves as we are dependent on God to give us His Life that saves.  Baptism is a choice we make as a believer.  This choice cannot be made for us by others so any form of baptism that takes place before we receive Jesus Christ is no substitute for the choice we need to make as full believers.

Ideally, believers should be baptised in water as soon as possible after receiving Jesus, as it frequently shuts off some problems and a lot of demonic interference.

The Bible contains some pictures and parables that give us clues as to the results of Baptism in water.  A passage from Exodus 29:4 talks about the washing of priests:  In the law of Moses, baptism or washing was about sanctification/cleansing for a task and about being inducted into the priesthood.  In the new covenant in Jesus Christ, baptism is about spiritual cleansing and sealing into the Family of God and the Kingdom of God as a priest-king.  It is primarily carried out as a step of obedience to Jesus' commands.  Even though all the results and reasons for it may not be fully understood by a believer at their time of baptism, it was spoken of in the New Testament as part of the salvation process rather than an optional extra.  God's response to our obedience and belief is to enable the fuller release of the resurrection life of Jesus Christ into and through our personal life.

Mark 16:16 He who believes and is baptised shall be saved; but he who does not believe shall be lost to hell.

Acts 2:38 -41  Men and brothers, what shall we do? Then Peter said unto them, Repent, and be baptised every one of you in the name of Jesus Christ for the forgiveness of your sins, and you shall receive the gift of the Holy Spirit.  For the promise is unto you, and to your children, and to all that are afar off, even as many as the Lord our God shall call. And with many other words he testified and encouraged them, saying, Save yourselves from this warped generation. Then they who gladly received his words were baptised: and that same day about three thousand souls were added to them .

1 Peter 3:18-22 For Christ also once suffered for sins, the just for the unjust, that he might bring us to God, indeed being put to death in the flesh, but made alive in the Spirit: in which also he went and preached to the spirits in prison; to disobeying ones, when once the longsuffering of God waited in the days of Noah, while the ark was being prepared (in which a few, that is, eight souls were saved through water);   which figure now also saves us, baptism; not a putting away of the filth of the flesh, but the answer of a good conscience toward God, by the resurrection of Jesus Christ;   Who is at the right hand of God, having gone into Heaven, where the angels and authorities and powers are being subjected to Him.

Acts 8:36-39 Philip and the Eunuch - Then Philip opened his mouth and began at the same Scripture and preached the gospel of Jesus to him. And as they passed along the way, they came on some water. And the eunuch said, See, here is water, what hinders me from being baptized? Philip said, If you believe with all your heart, it is lawful. And he answered and said, I believe that Jesus Christ is the Son of God.
And he commanded the chariot to stand still. And they both went down into the water, both Philip and the eunuch. And he baptized him.
And when they had come up out of the water, the Spirit of the Lord caught Philip away, so that the eunuch saw him no more. And he went on his way rejoicing.

Acts 10:47 - Can anyone forbid water that these, who have received the Holy Ghost as well as we, should not be baptised?
Acts 19:4-5 - And Paul said, John truly baptised with the baptism of repentance, saying to the people that they should believe into Him coming after him, that is, into Jesus Christ. And hearing, they were baptised in the name of the Lord Jesus.
Acts 22:16 - And now what do you intend? Arise and be baptised and wash away your sins, calling on the name of the Lord.

Questions sometimes asked:

1) What does baptism mean?    

Baptism is about:

a) remission (or forgiveness and washing away) of sins;
b) a full release of the ability to life-shift from our old self life to resurrection life;
c) priesthood of all believers. 

Hebrews 3:1 -  Therefore, holy brothers, called to be partakers of the heavenly calling, consider the Apostle and High Priest of our profession, Christ Jesus,
1 Peter 2:5 - you also as living stones are built up a spiritual house, a holy priesthood, to offer up spiritual sacrifices acceptable to God through Jesus Christ.
Hebrews 12:2 - looking to Jesus the Author and Finisher of our faith, who for the joy that was set before Him endured the cross, despising the shame, and sat down at the right of the throne of God.
1 Peter 2:21 -  For you were not called to this? For Christ also suffered on our behalf, leaving us an example, that you should follow His steps,
Revelation 1:6 - and made us kings and priests to God and His Father, to Him be glory and dominion forever and ever. Amen.

Jesus was baptised high priest by John in the river Jordan.  As we are baptised we become priests under His high priesthood.

The old self life is death and there is no life in it. John 3:36
The only Life is from God John  4:14,  John  5:24,  John 6:33-40

Before baptism, the results of Jesus' entry into our lives after our surrender to Him are:

1) creation of His new life in us (spoken of by Paul as our "new man"), and

2) the separation of our identity from our "old nature" or "self" so we can be free to choose moment by moment between self and spirit, and which one we are going to listen to.

John 8:12 -Then Jesus spoke again to them, saying, I am the Light of the world. He who follows Me shall not walk in darkness, but shall have the light of life.

•    Baptism is a symbol of dying / death to self/"flesh" (not the physical flesh, but the carnal nature) and being raised up in new resurrection Life - His resurrection Life given to us as an exchange for our sin and sinful nature.  What an amazing gift!!

•    Allowing our bodies to be lowered under water and raised up out of it is an act of surrender in obedience to God.  God recognises this obedience and releases His power in freeing ways, making baptism a prophetic act.

•    The power of God is released at baptism to disempower the old "flesh" or self man nature, and to empower the new Jesus Christ shaped creation to be able to take over.  Problems, hassles and fears - and many demonic based problems - that seemingly could not be overcome previously, can disappear after this step of obedience is carried out.

2) Is there a difference between being baptised "in the name of Jesus Christ" and being baptised "in the name of the Father, the Son and the Holy Spirit"?  Different descriptions are given in Matthew 28:16,  John 17:6-8 Acts 1:5 so it would appear that the early Christians understood that either form was valid.  Differences today can happen because of our differing expectations and beliefs.  The main emphasis in the New Testament is about belief in God and obedience to Jesus' commands.

3) When should baptism happen?

For the above reasons, among others, baptism should take place as soon as possible after salvation is experienced.  Certainly in the Book of Acts, people were baptised very shortly after being saved/converted.

Some more references for you to get the strength of it.  Please do this in context meditatively (thinking about it and all the stuff around it).

Matthew 3:7 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?
Matthew 20:22-23 But Jesus answered and said, Ye know not what ye ask. Are ye able to drink of the cup that I shall drink of, and to be baptised with the baptism that I am baptised with? They say unto him, We are able.
And he saith unto them, Ye shall drink indeed of my cup, and be baptised with the baptism that I am baptised with: but to sit on my right hand, and on my left, is not mine to give, but it shall be given to them for whom it is prepared of my Father.

Matthew 21:25 The baptism of John, whence was it? from heaven, or of men? And they reasoned with themselves, saying, If we shall say, From heaven; he will say unto us, Why did ye not then believe him?
Matthew 28:16 Go ye therefore, and teach all nations, baptising them in the name of the Father, and of the Son, and of the Holy Ghost:

Mark 1:4 John did baptise in the wilderness, and preach the baptism of repentance for the remission of sins.
Mark 10:38-39 But Jesus said unto them, Ye know not what ye ask: can ye drink of the cup that I drink of? and be baptised with the baptism that I am baptised with?
And they said unto him, We can. And Jesus said unto them, Ye shall indeed drink of the cup that I drink of; and with the baptism that I am baptised withal shall ye be baptised:

Mark 11:30 The baptism of John, was it from heaven, or of men? answer me.
Mark 16:16 He that believeth and is baptised shall be saved; but he that believeth not shall be damned. Luke 3:3 And he came into all the country about Jordan, preaching the baptism of repentance for the remission of sins;

Luke 7:29 And all the people that heard him, and the publicans, justified God, being baptised with the baptism of John.
Luke 12:50 But I have a baptism to be baptised with; and how am I straitened till it be accomplished!
Luke 20:4 The baptism of John, was it from heaven, or of men?
Acts 1:22 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.
Acts 2:38-41 Men and brethren, what shall we do?  Then Peter said unto them, Repent, and be baptised every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.  For the promise is unto you, and to your children, and to all that are afar off, even as many as the Lord our God shall call.  And with many other words did he testify and exhort, saying, Save yourselves from this untoward generation.  Then they that gladly received his word were baptised: and the same day there were added unto them about three thousand souls.

Acts 10:37 That word, I say, ye know, which was published throughout all Judaea, and began from Galilee, after the baptism which John preached;
Acts 13:24 When John had first preached before his coming the baptism of repentance to all the people of Israel.
Acts 18:25 This man was instructed in the way of the Lord; and being fervent in the spirit, he spake and taught diligently the things of the Lord, knowing only the baptism of John.
Acts 19:3 And he said unto them, Unto what then were ye baptised? And they said, Unto John's baptism.
Acts 19:4 Then said Paul, John verily baptized with the baptism of repentance, saying unto the people, that they should believe on him which should come after him, that is, on Christ Jesus.

Acts 22:16 And now why tarriest thou? arise, and be baptised, and wash away thy sins, calling on the name of the Lord.
Romans 6:4 Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life.
Ephesians 4:5 One Lord, one faith, one baptism,
Colossians 2:12 Buried with him in baptism, wherein also ye are risen with him through the faith of the operation of God, who hath raised him from the dead.
1 Peter 3:21 The like figure whereunto even baptism doth also now save us (not the putting away of the filth of the flesh, but the answer of a good conscience toward God,) by the resurrection of Jesus Christ: