Latter-day Saints "believe that the first principles and ordinances of the gospel are: first, Faith in the Lord Jesus Christ; second, Repentance; third, Baptism by immersion for the remission of sins; fourth, Laying on of hands for the gift of the Holy Ghost." We also "believe that a man must be called of God, by prophecy, and by the laying on of hands by those who are in authority, to preach the gospel and administer in the ordinances thereof" (Articles of Faith 4 & 5).
In other words, after a person believes in Jesus Christ, repents, and is baptized by immersion, the gift of the Holy Ghost is bestowed by the laying on of hands by those who are in authority to do so.
I have known some good Christian people that have believed that the gift of the Holy Ghost is bestowed on an individual at the moment he believes without reference to baptism or the laying on of hands. I will here argue that such an idea is inconsistent with the Biblical record while the LDS view is more consistent.
First, on the day of Pentecost, Peter preached a powerful sermon that was well received. The Holy Ghost bore record to his audience that Jesus was indeed "both Lord and Christ." After he had preached, the people "were pricked in their heart, and said unto Peter and to the rest of the apostles, Men and brethren, what shall we do?" (Acts 2:37). Clearly, they began to exercise faith in Jesus Christ by believing Peter's message. They wanted to know what they should do. If the doctrine of being saved by saying the sinner's prayer were indeed true, this would have been the perfect time for Peter to say something like "Pray to Jesus and ask him to forgive you and you will be saved," but what did he say?
"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 2:38).
These people who had 1) Faith in Jesus Christ were told to 2) Repent 3) be baptized for the remission of sins and that 4) they would then receive the gift of the Holy Ghost. This is clearly incompatible with the idea that you receive the Holy Ghost after simply believing or saying the "sinner's prayer." If ever Peter had the opportunity to teach such a doctrine, here it was. He didn't teach such a doctrine, however, but he taught one that is entirely consistent with the LDS article of faith mentioned above.
One could attempt to argue that this was the prescribed method for being saved and receiving the gift of the Holy Ghost for this particular group of people but that ti isn't required of all people at all times. However, Peter makes certain that this isn't the case by what he said next:
"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" (Acts 2:39).
He then exhorted them to "save [themselves] from this untoward generation. Then they that gladly received his word were baptized..." (Acts 2:40-41). Once again, baptism was the door to salvation. In order to "save themselves" they must not stop with faith alone or with repentance, but also be baptized. (I digress)
Another fascinating insight comes from Acts 8.
"But when they believed Philip preaching the things concerning the kingdom of God, and the name of Jesus Christ, they were baptized, both men and women.
13 Then Simon himself believed also: and when he was baptized, he continued with Philip, and wondered, beholding the miracles and signs which were done.
14 Now when the apostles which were at Jerusalem heard that Samaria had received the word of God, they sent unto them Peter and John:
15 Who, when they were come down, prayed for them, that they might receive the Holy Ghost:
16 (For as yet he was fallen upon none of them: only they were baptized in the name of the Lord Jesus.)
17 Then laid they their hands on them, and they received the Holy Ghost.
18 And when Simon saw that through laying on of the apostles’ hands the Holy Ghost was given, he offered them money,
19 Saying, Give me also this power, that on whomsoever I lay hands, he may receive the Holy Ghost.
20 But Peter said unto him, Thy money perish with thee, because thou hast thought that the gift of God may be purchased with money."
This is significant for several reasons. First, these people in Samaria already believed on Jesus' name and were baptized, yet they hadn't received the Holy Ghost. Only did they receive this gift after Peter and John came and laid hands on them to give them the gift. Simon saw that this gift was given this way and offered to buy the gift from the apostles.
If the gift of the Holy Ghost comes just through belief in Jesus, why didn't these Samaritans receive that gift the moment they believed? Also, why didn't Philip give them the gift? He apparently baptized them, but didn't lay hands on them. Why?
According to LDS doctrine, a person who hold Aaronic priesthood can baptize but cannot confer the gift of the Holy Ghost. However, apostles or elders can confer the gift of the Holy Ghost. This story makes perfect sense from an LDS doctrinal standpoint: Philip had authority to baptize but he didn't have authority to confer the gift of the Holy Ghost. The apostles then came and conferred this gift on the recently baptized believers.
There are many other such examples, but suffice it to say these scriptures seem to imply that a person must:
1) have faith in Jesus
3) be baptized for the remission of sins
4) receive the Holy Ghost by the laying on of hands by those who have authority
5) some have authority to baptize but do not have authority to bestow the gift of the Holy Ghost.
LDS belief is entirely consistent with these scriptures. Is the rest of modern Christianity?
For further clarification, LDS believe individuals may receive manifestations of the Holy Ghost prior to baptism to strengthen faith in Christ and to bring people to repentance and baptism. There are several instances of people receiving such manifestations of the Holy Ghost in scripture and outside of scripture. If a person rejects such manifestations, however, the Holy Ghost will not abide with him. On the other hand, if a person follows such manifestations he will eventually find himself with faith, having been baptized, and having the gift of the Holy Ghost sealed upon his head.