You must "do the things which I have told you I have seen that your Lord and your Redeemer should do." You must "follow Him." There is no other way nor name given under heaven to obtain salvation. (Mosiah 5: 8.)
It was for this reason Nephi was "shown" these things. The Lord and His Father taught Nephi so he could in turn teach others, including us. The message was intended to save many, not just Nephi. But we must give heed to the message when we hear it.
The "gate by which ye should enter is repentance and baptism by water." You must repent first. Then, having repented, receive baptism by water. When this is done, "then cometh a remission of your sins by fire and by the Holy Ghost."
Without the "fire" to purge the sacrifice upon the altar, it is not cleansed. It cannot become holy unless exposed to that fire.
But note - this is automatic. It is not by the laying on of hands. The laying on of hands for the gift of the Holy Ghost is not required in this teaching. Nephi, with elaboration from the Father and the Son, is teaching that this is an event that follows the process of "repentance and baptism by water." That is, the ordinance of baptism, when accompanied by repentance and done right, is the reason for this event.
Laying on of hands is for "the gift of the Holy Ghost" so there may be a companion and guide for a person. This is an ordinance. It is also the moment one is confirmed a member of the church. But it is not necessarily co-equal with receiving "fire and the Holy Ghost" as described here. There is nothing that excludes it from being coincidental in time, however. They may happen at the same moment. That is, after baptism, and while receiving the laying on of hands, one may receive both the gift of the Holy Ghost, and also fire and the Holy Ghost. As a result one is renewed in the manner described in this chapter. They are not co-equal.
Laying on of hands does not appear to be an ordinance in the Book of Mormon until the coming of Christ in 3 Nephi. The only potential exception is found in Alma 31: 36, where Alma "clapped his hands upon them who were with him" and they received the Holy Ghost. This is similar to the Lord "breathing" the Holy Ghost upon His disciples. (John 20: 22.) They were instructed to lay on hands, and would perform that act rather than breathing upon those who were to receive the Holy Ghost. The ordinance is different from "clapping" or from "breathing" and involves the process we follow in the church today. (D&C 33: 15.)
The baptism of fire and the Holy Ghost promised here is given without man's involvement, comes from heaven, is promised by both the Father and the Son. It is a signal of redemption, purification and holiness. It is included in the "gate" for entering into God's presence. For God is a "consuming fire" and those who enter into that presence must be able to endure that fire. (Heb. 12: 29; see also Deu. 4: 24.) Without the capacity to do so, a person would be consumed by the flames. (Lev. 10: 1-2.) The fire and the Holy Ghost are also given as a sign to the recipient that they may know it is safe for them to enter into God's presence and not be consumed. In earlier versions of the First Vision, Joseph described the "pillar of light" as a "pillar of fire" which gradually descended. He wondered if the trees would be consumed as it descended, but seeing they were not he thought it safe for him to be exposed to it as well. When it fell upon him, the vision opened up and he saw the Father and the Son.
Christ also entered into this glorious light on the Mount of Transfiguration. (Matt. 17: 1-2.)
We are to do as Nephi instructs, "do the things which I have told you I have seen that your Lord and your Redeemer should do; for, for this cause have they been shown unto me, that ye might know the gate by which ye should enter."
We live below the standard Christ set for us. We needn't. Have faith. Press forward feasting on His words. You can and will find Him there.