There is no question that the Savior said, as recorded in Mark, that those who believe AND are baptized will be saved. There are undoubtedly numerous p***ages in the scriptures where the Lord provides discrete elements necessary for salvation. As our Evangelical friends are constantly reminding us, we must read the scriptures as a whole in order to get the whole picture. The whole picture is that there are a lot of things that we have to do for salvation. We must do the will of the Father. We must have faith in Christ. We must keep the commandments. We must forgive one another. We must be peacemakers. We must be meek. And the list goes on.

We cannot in good conscience simply count up the number of times that Christ articulated one of the requirements for salvation, and conclude that it is the only thing required. Indeed, as I will show below, there is a very good reason why a single element, faith in Christ, is emphasized above other requirements. But in the meantime, remember that John himself said,
And there are also many other things which Jesus did, the which, if they should be written every one, I suppose that even the world itself could not contain the books that should be written.

John 21:25
In other words, it is foolhardy to think that each of the writers of the Gospel, in reciting the words of the Savior, would try to make a comprehensive list of the requirements for salvation every time they mention one of the requirements.

The requirement of baptism is not simply a matter of obedience. No where does the Holy Bible diminish the importance of baptism from a requirement for salvation to merely an optional expression of obedience. Although, even if one wants to try and make the argument that "[b]aptism is a matter of obedience," do they seriously want to argue that one can be saved without being obedient? What did Christ say?
Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven.

Matthew 7:21
According to the Savior of the World, salvation comes only to those who are obedient. That places baptism squarely in the the column of requirements for salvation; to argue otherwise is to make Christ out to be a liar.

Christ Himself set the example, showing with undeniable force the necessity of baptism, when He, the Savior of the World, humbled Himself and submitted to baptism at the hand of John the Baptist:
13 Then cometh Jesus from Galilee to Jordan unto John, to be baptized of him.
14 But John forbad him, saying, I have need to be baptized of thee, and comest thou to me?
15 And Jesus answering said unto him, Suffer it to be so now: for thus it becometh us to fulfil all righteousness. Then he suffered him.
16 And Jesus, when he was baptized, went up straightway out of the water: and, lo, the heavens were opened unto him, and he saw the Spirit of God descending like a dove, and lighting upon him:
17 And lo a voice from heaven, saying, This is my beloved Son, in whom I am well pleased.

Matthew 3
Christ did not do this to establish a broad gate wherein one may enter for salvation. He did it to show how narrow the way is by doing it Himself. HE SHOWED US THE WAY!

We are indebted to Nephi for expounding on why Christ submitted to baptism.
6 And now, I would ask of you, my beloved brethren, wherein the Lamb of God did fulfil all righteousness in being baptized by water?
7 Know ye not that he was holy? But notwithstanding he being holy, he showeth unto the children of men that, according to the flesh he humbleth himself before the Father, and witnesseth unto the Father that he would be obedient unto him in keeping his commandments.

2 Nephi 31
Obedience is an inescapable theme in every single volume of scripture, beginning with Adam and Eve in the Garden and ending with the martyrdom of the Prophet Joseph Smith. The disobedient can not be saved.

Christ's final charge to the Apostles, as he ascended into heaven was,
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:
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

Matthew 28
For Christ, the most important things He wanted His Apostles to do in His absence was to teach obedience and to baptize. Why would anyone want to take away from the Word of God by saying that baptism is not required for salvation? Such a creed is rightly called an abomination and corruption by our Savior.

After the ascension, as the Apostles went about preaching Christ, baptism was taught as a necessary companion to faith.
37 Now when they heard this, they were *****ed in their heart, and said unto Peter and to the rest of the apostles, Men and brethren, what shall we do?
38 Then Peter said unto them, Repent, and be baptized 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.

Acts 2
Peter did not say, Just have faith. He didn't say, Ya gotta believe. NO! He said, Repent and be baptized. How difficult is that to understand?

Now, I should say a word about the emphasis that John seems to place on Christ's words to the effect that those who believe will be saved. John was very pointed about what he thought about people who claimed they had faith but were not obedient:
3 And hereby we do know that we know him, if we keep his commandments.
4 He that saith, I know him, and keepeth not his commandments, is a liar, and the truth is not in him.

1 John 2
For John, it was simple. If you have faith, you will be obedient. You will be baptized. It was unnecessary for John, in reciting the words of Christ, to go beyond declaring the necessity of faith because true faith would lead to obedience to the other commandments, like baptism. For John, baptism was not optional. It was a self-evident requirement for salvation because it would naturally follow true faith.

One of the plain and precious things that I have no doubt the Savior taught in Galilee, but which has been lost in the Holy Bible, has been restored in the Book of Mormon. One of the very first thing the Savior taught the Nephites and Lamanites who were gathered at Zarahemla when He visited them was the necessity of baptism.
33 And whoso believeth in me, and is baptized, the same shall be saved; and they are they who shall inherit the kingdom of God.
34 And whoso believeth not in me, and is not baptized, shall be ****ed.

3 Nephi 11
The Book of Mormon contains the words of Christ. It testifies of Him, and is a testimony of the great love the Father has for His children, in that He preserved to come forth in the last days to stand as a witness for truth and to persuade men to come unto Christ and baptized. By the same token it will stand as a witness against the ungodly and those who despise His power to their everlasting shame.