The Aaronic Priesthood was restored to the earth by John the Baptist on May 15, 1829. Between then and May 1830, the Melchizedek Priesthood was also restored by the ancient apostles Peter, James and John.
The priesthood provides two things: power and authority. Authority to govern the Church, perform ordinances, and organize is very important. As important as authority is, however, it is impotent without the power of the priesthood. President Packer recently stated that we do well on distributing the authority, but need to improve on distributing the true powers of heaven. He also notes in his discussion on priesthood,
"I include the sisters because it is crucial for everyone to understand what is expected of the brethren. Unless we enlist the attention of the mothers and daughters and sisters—who have influence on their husbands, fathers, sons, and brothers—we cannot progress. The priesthood will lose great power if the sisters are neglected." (Ensign, April 2010, The Power of the Priesthood)
This power is not only for the men, but also for the women of the Church. Why? Because of the ordinances and covenants attached to the priesthood.
The Aaronic Priesthood provides the outward ordinances, holding the keys of repentance, baptism and the ministering of angels (D&C 13). The greater Priesthood of Melchizedek holds even greater power and promise:
"And this greater priesthood administereth the gospel and holdeth the key of the mysteries of the kingdom, even the key of the knowledge of God.
Therefore, in the ordinances thereof, the power of godliness is manifest.
And without the ordinances thereof, and the authority of the priesthood, the power of godliness is not manifest unto men in the flesh;
For without this no man can see the face of God, even the Father, and live.
Now this Moses plainly taught to the children of Israel in the wilderness, and sought diligently to sanctify his people that they might behold the face of God;
But they hardened their hearts and could not endure his presence; therefore, the Lord in his wrath, for his anger was kindled against them, swore that they should not enter into his rest while in the wilderness, which rest is the fulness of his glory. (D&C 84:19-24)
While the Aaronic Priesthood gives the power to have angels minister to a person and to have a remission of sins, the Melchizedek Priesthood holds the power to bring people into the presence of God, to have His mystery revealed to them, and to become not only cleansed of sin, but purified to a divine state!
Moses' goal at Sinai was to take Israel to the top of the mountain, where each one of them would see God personally. They refused to go, fearing God's wrath and reluctant to give up their sinful ways. God gave them the lesser priesthood as a preparatory power, to prepare them for the greater opportunities. If mankind was not ready to converse with God, perhaps they could be prepared to converse with angels.
The Melchizedek Priesthood, however, contains the power, primarily through the ordinances, of being in the presence of the members of the Godhead.
First, the Gift of the Holy Ghost is confirmed upon a person, giving that person access to the third member of the Godhead. In the temple ordinances, which set us apart from the world both figuratively and literally, we learn to walk through the Cosmos and all of Creation, in a journey to return back into the full presence and glory of God. This is not a journey that is accomplished alone. It is a journey for both Adam and Eve, husband and wife, who share the power, authority and blessings of the Melchizedek Priesthood within the temple. In the marriage sealing, husband and wife both receive together the Patriarchal Priesthood, the greatest role in the Melchizedek Priesthood. Husband and wife are promised that as they are faithful to God, they will receive blessings in time and eternity, to stand in God's presence and be like Him.
This is the purpose of the priesthood in our day: to prepare a people to stand in the presence of God and be holy. Through the ordinances the priesthood provides, men and women can enjoy the greatest blessings and opportunities of God in heaven. These promises begin with baptism and find the climax as the believers enter into the Celestial Room of the temple, symbolic of the day when they literally will walk into the Celestial Kingdom and into the presence of God the Father and Jesus Christ.