Alma 13:16 - 13:20
Alma 13:16 Now these ordinances were given after this manner, that thereby the people might look forward on the Son of God, it being a type of his order, or it being his order, and this that they might look forward to him for a remission of their sins, that they might enter into the rest of the Lord.
The power given to Melchizedek to administer the ordinances to his people and the manner which they were to be administered would be the same as if the Son of God had done so. It would be a lesson on how they should be done. The end result of the ordinances was for us all to receive a remission of our sins and be worthy to return to live with God.
Alma 13:17 Now this Melchizedek was a king over the land of Salem; and his people had waxed strong in iniquity and abomination; yea, they had all gone astray; they were full of all manner of wickedness;
Melchizedek was the king of Salem or the land of Salem. The people of that land, however, were evil, all of them. They were as bad a people as you can get.
Alma 13:18 But Melchizedek having exercised mighty faith, and received the office of the high priesthood according to the holy order of God, did preach repentance unto his people. And behold, they did repent; and Melchizedek did establish peace in the land in his days; therefore he was called the prince of peace, for he was the king of Salem; and he did reign under his father.
But Melchizedek went to work and started to preach repentance to the people. Low and behold, they repented. A peaceful order was restored in the land and he was now called the prince of peace because of what the effect of his efforts. He was king and ruled under his father’s direction.
Some LDS scholars think that Melchizedek was Shem the son of Noah. Abraham was born while Shem was still alive as was Noah, himself. I’m sure Abraham must have known them both. Reading the Book of Abraham the desire to have the blessing of the fathers must have come from both knowing these men and being taught by them. It is interesting that Abraham had been dead for 35 years when Shem died. Like I say many LDS scholars think that Shem was Melchizedek. Looks like Shem was a greater individual then we can perceive for the Bible.
Alma 13:19 Now, there were many before him, and also there were many afterwards, but none were greater; therefore, of him they have more particularly made mention.
Melchizedek was considered one of the greatest prophets who ever lived. This is considering those who were his ancestors and descendants. That is why the scriptures talk about him.
At least ours talk about him. He is hardly mentioned in the Old Testament.
Alma 13:20 Now I need not rehearse the matter; what I have said may suffice. Behold, the scriptures are before you; if ye will wrest them it shall be to your own destruction.
Now if the people of Ammonihah want to try and minimalize the scriptures that talk about him and what he was able to accomplish, they do so at their own peril.