Is baptism essential for salvation?

The biblical answer is YES! Many people these days believe that salvation comes by "grace alone through faith alone". The only way we have to understand salvation and how to receive it is defined in the New Testament, which is what we are going to look at in this study. The most important part of any Bible study is the use of the Bible. In this (and basically all of my posts) I will be using the NIV Translation because it is easiest for me to understand, although I will occasionally use other translations that I believe explain or state something in a better or clearer manner.

With that introduction out of the way, let us begin with a message regarding false teachings and understanding of the Scripture.

In 2 Thessalonians 2:9-12, Paul writes:
9The coming of the lawless one will be in accordance with the work of Satan displayed in all kinds of counterfeit miracles, signs and wonders, 10and in every sort of evil that deceives those who are perishing. They perish because they refused to love the truth and so be saved. 11For this reason God sends them a powerful delusion so that they will believe the lie 12and so that all will be condemned who have not believed the truth but have delighted in wickedness.

When any Scripture is taken out of context, it can be made (much like statistics) to say whatever the false teacher wants. Everyone should open their Bible and read in order to understand the Scriptures for themselves because the Bible is written so that anyone who reads it can understand it. As we see in 1 Corinthians 2:12, which says:
12We have not received the spirit of the world but the Spirit who is from God, that we may understand what God has freely given us.

Now onto baptism as being essential:

Matthew 28:18-20
18Then Jesus came to them and said, "All authority in heaven and on earth has been given to me. 19Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, 20and teaching them to obey everything I have commanded you. And surely I am with you always, to the very end of the age."

Because Christ has been given all authority on Earth and in Heaven, when He says to go make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, and then says to teach those disciples to obey everything He has commanded, then we as disciples must go teach other non-believers the Gospel and baptize them in the name of the Father and the Son and the Holy Spirit, and then teach them to do the same.

Mark 16:15-16
15He said to them, "Go into all the world and preach the good news to all creation. 16Whoever believes and is baptized will be saved, but whoever does not believe will be condemned.

The Scripture says that we must preach the good news (the Gospel) to all creation, and then whoever believes and is baptized will be saved. The Scripture says that we must not only believe, but then we must be baptized in order to be saved. Then upon baptism we will be saved. If we do not believe, what purpose is there in being baptized? For this non-belief would mean we have condemned ourselves.

Now, there are those who believe that this baptism is not referring to the physical baptism in water, but the Greek uses βαπτ
ζω,v  \{bap-tid'-zo} 
1) to dip repeatedly, to immerse, to submerge (of vessels sunk)  2) to cleanse by dipping or submerging, to wash, to make clean  with water, to wash one's self, bathe  3) to overwhelm. 

With this definition we see that this is clearly meant as a physical baptism. Another point is that some believe that this Scripture should not, or cannot, be used as a proof for the necessity of baptism because it does not appear in some of the earliest manuscripts, but the reason it has not been removed from the Bible is because it is in harmony with all the other Scriptures that teach about baptism and therefore does not contradict what the Scripture clearly teaches. 

Baptism is used in other scriptures as well. The definition of baptism is:
βπτισμα,n  \{bap'-tis-mah}
1) immersion, submersion 1a) of calamities and afflictions with which one is quite overwhelmed 1b) of John's baptism, that purification rite by which men on  confessing their sins were bound to spiritual reformation, obtained the pardon of their past sins and became qualified for the benefits of the Messiah's kingdom soon to be set up. This was valid Christian baptism, as this was the only baptism the apostles received and it is not recorded anywhere that they were ever re-baptized after Pentecost. 1c) of Christian baptism; a rite of immersion in water as commanded by Christ, by which one after confessing his sins and professing his faith in Christ, having been born again by the Holy Spirit unto a new life, identifies publicly with the fellowship of Christ and the church.  

This definition of baptism is used the same way, and has the same meaning in all of the following verses.

Matthew 3:7
 7But when he saw many of the Pharisees and Sadducees coming to where he was baptizing, he said to them: "You brood of vipers! Who warned you to flee from the coming wrath?

Matthew 21:25
25John's baptism—where did it come from? Was it from heaven, or from men?"

Mark 1:4
4And so John came, baptizing in the desert region and preaching a baptism of repentance for the forgiveness of sins.

Mark 10:38-39
 38"You don't know what you are asking," Jesus said. "Can you drink the cup I drink or be baptized with the baptism I am baptized with?"
 39"We can," they answered. Jesus said to them, "You will drink the cup I drink and be baptized with the baptism I am baptized with,

Mark 11:30
30John's baptism—was it from heaven, or from men? Tell me!"

Luke 3:3
3He went into all the country around the Jordan, preaching a baptism of repentance for the forgiveness of sins.

Luke 7:29
 29(All the people, even the tax collectors, when they heard Jesus' words, acknowledged that God's way was right, because they had been baptized by John.

Luke 12:50
50But I have a baptism to undergo, and how distressed I am until it is completed!

Luke 20:4
4John's baptism—was it from heaven, or from men?"

Acts 1:22
22beginning from John's baptism to the time when Jesus was taken up from us. For one of these must become a witness with us of his resurrection."

Acts 10:37
37You know what has happened throughout Judea, beginning in Galilee after the baptism that John preached—

Acts 13:24
24Before the coming of Jesus, John preached repentance and baptism to all the people of Israel.

Acts 18:25
25He had been instructed in the way of the Lord, and he spoke with great fervor and taught about Jesus accurately, though he knew only the baptism of John.

Acts 19:03-4
 3So Paul asked, "Then what baptism did you receive?"
      "John's baptism," they replied.
 4Paul said, "John's baptism was a baptism of repentance. He told the people to believe in the one coming after him, that is, in Jesus."

Romans 6:4
4We were therefore buried with him through baptism into death in order that, just as Christ was raised from the dead through the glory of the Father, we too may live a new life.

Ephesians 4:5
5one Lord, one faith, one baptism;

1 Peter 3:21
21and this water symbolizes baptism that now saves you also—not the removal of dirt from the body but the pledge of a good conscience toward God. It saves you by the resurrection of Jesus Christ,

Some of these scriptures reference the baptism from John, but those that do not specifically reference John’s baptism, must be something more than just baptism of repentance. We see this quite clearly from 1 Peter 3:21 where Peter explains that the baptism that now saves us is a presentation of us before God with a clear conscience, through Jesus' resurrection. In no way does this even seem to mean that we are saved before having been baptized and then in order to show off that we are saved we then get baptized, as some would have us believe.