The prince of peace
Since the beginning of creation, the Lord has blessed his faithful people with the priesthood. This delegation of authority is a sacred trust shared between God and his servants, and it's unending blessings allow his chosen people to officiate in the ordinances which he has set out for the redemption of mankind.
In the days of Moses God bestowed the lower priesthood to Aaron and his sons, and with that priesthood came the law of sacrifice, and the Mosaic dietary laws. They were commanded to build a tabernacle with sections that lead to a holy place where the Lord God resided. It was a very sacred place and only the priests were allowed to enter.
Before Moses came along there were the patriarchs who were the leaders of the ancient Hebrews. One of the first patriarchs was Abraham, and though he was a prophet of God, he submitted his will to the lord and tithed to the high priest Melchizedek. Melchizedek was only briefly mentioned in the old testament but the priesthood which he held was spoken of in the writings of Paul who declared that Jesus was the "high priest after the order of Melchizedek", and thus the only sacrifice that was needed of this higher priesthood was the final sacrifice of Christ, whereas the Levitical, or Aaronic priesthood required constant sacrifice.
Shortly after the atoning sacrifice of Jesus Christ, the children of Israel were scattered and the priesthood was lost. The temple as well was destroyed and no more were they able to perform animal sacrifice to atone for their sins. Likewise shortly after the martyrdom of Jesus' apostles, the priesthood which he bestowed on them was lost as well, and thus the words of the prophet Amos were fulfilled;
"Behold, the days come, saith the Lord GOD, that I will send a famine in the land, not a famine of bread, nor a thirst for water, but of hearing the words of the LORD: And they shall wander from sea to sea, and from the north even to the east, they shall run to and fro to seek the word of the LORD, and shall not find it. In that day shall the fair virgins and young men faint for thirst." -Amos
The apostle Paul also spoke of a falling away, along with Matthew who saw this falling away unfolding in his very day; "For this people's heart is waxed gross, and their ears are dull of hearing, and their eyes they have closed"
So we see that the Lord said the priesthood was going to be lost, and then those words were fulfilled.
Following the apostasy and the subsequent loss of the priesthood there was a need for a restoration of the priesthood. The restoration of the priesthood is the divine truth that men cannot obtain this delegation of authority from God without the permission of he who holds it.
Thus we see in the scriptures that the famine will be ended through angelic ministry,
And I saw another angel fly in the midst of heaven, having the everlasting gospel to preach unto them that dwell on the earth, and to every nation, and kindred, and tongue, and people" -Revelation 14:6
And Elijah will restore the priesthood,
"And Jesus answered and said unto them, Elias truly shall first come, and restore all things." -Matthew 17:11
because Jesus said it will happen,
"When they therefore were come together, they asked of him, saying, Lord, wilt thou at this time restore again the kingdom to Israel?
And he said unto them, It is not for you to know the times or the seasons, which the Father hath put in his own power." Acts 1;6-7
"Repent ye therefore, and be converted, that your sins may be blotted out, when the times of refreshing shall come from the presence of the Lord.And he shall send Jesus Christ, which before was preached unto you: Whom the heaven must receive until the times of restitution of all things, which God hath spoken by the mouth of all his holy prophets since the world began." Acts 3:19-21
And in the last days he will gather in the house of Israel,
"That in the dispensation of the fulness of times he might gather together in one all things in Christ, both which are in heaven, and which are on earth; even in him" -Ephesians 1:10
Along with the restoration of the priesthood comes the restoration of the temple,
"And it shall come to pass in the last days, that the mountain of the LORD's house shall be established in the top of the mountains, and shall be exalted above the hills; and all nations shall flow unto it." -Isaiah 2:2
But there will no longer be a need for animal sacrifice in the temple, so we will have to preform ordinances in behalf of the dead who were not baptized under the authority of Jesus Christ since clearly the resurrection of the body is spoken of in the Bible and Jesus said that no one can receive the kingdom of heaven without being baptized.
Else what shall they do which are baptized for the dead, if the dead rise not at all? why are they then baptized for the dead? And why stand we in jeopardy every hour?
Thus the need for the restoration of the priesthood, otherwise we cannot, through our own merits, extend that power to bless the lives of believers in Christ. It is the only power that reaches beyond the veil of death, it is the priesthood of God which binds in heaven the things that are bound on Earth, without it there is no authority to perform the ordinances which God has commanded us to partake in. it is the authority to bless, and to baptize, to heal the sick, and to serve God in our greatest capacity.