Dispensation
A dispensation of the gospel is a time period, of no particular length, during which the Lord has at least one authorized servant on the earth who holds the keys of the holy priesthood, and who has a divinely appointed commission to "dispense" the gospel to mankind. When a new dispensation is organized, the Lord reveals the gospel anew, so that mankind is blessed with current revelation and does not have to depend upon previous dispensations for their knowledge of the gospel and the plan of salvation.
Dispensations are often associated with the servant who stands at the head of it. In Old Testament times, Adam, Enoch, Noah, Abraham, and Moses are all considered heads of new dispensations. When Jesus Christ came to earth He ushered in another dispensation. In the last days, the Lord called the Prophet Joseph Smith to usher in what is known as the "dispensation of the fulness of times."
Additionally, it is known that there were dispensations of the gospel among the Nephites and Jaredites in the Book of Mormon, as well as among the Lost Tribes of Israel. Melchizedek, after whom the Melchizedek Priesthood is called, could also be included as the head of a dispensation, as could John the Baptist. Both these men held the holy priesthood, taught the gospel to the people, and were unique in their time. There are many other prophets of the Lord who held the priesthood and knew of the gospel. Although little is known about them, such men as Abel, Esaias, Gad, Jeremy, Elihu, Caleb, Jethro, Zenock, and Zenos might also have been heads of dispensations.
Each of the dispensations has been characteristic in some way or other. Adam, for instance, opened the way for man to come to the earth; Enoch's people were taken to heaven; Jesus atoned for mankind and was resurrected; and Joseph Smith laid the foundation for a culmination God's work on the earth. While the Bible does contain some historical information about prophets and patriarchs of the Old Testament, it is latter-day revelation that clearly shows that the leaders of former dispensations all had the gospel of Jesus Christ and were called and ordained of Him.
Scriptures
Acts 3:20-21 20 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.
Ephesians 1:10 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:
D&C 27:13 Unto whom I have committed the keys of my kingdom, and a dispensation of the gospel for the last times; and for the fulness of times, in the which I will gather together in one all things, both which are in heaven, and which are on earth;
D&C 128:18, 21 18 For it is necessary in the ushering in of the dispensation of the fulness of times, which dispensation is now beginning to usher in, that a whole and complete and perfect union, and welding together of dispensations, and keys, and powers, and glories should take place, and be revealed from the days of Adam even to the present time. And not only this, but those things which never have been revealed from the foundation of the world, but have been kept hid from the wise and prudent, shall be revealed unto babes and sucklings in this, the dispensation of the fulness of times.
21 And the voice of Michael, the archangel; the voice of Gabriel, and of Raphael, and of divers angels, from Michael or Adam down to the present time, all declaring their dispensation, their rights, their keys, their honors, their majesty and glory, and the power of their priesthood; giving line upon line, precept upon precept; here a little, and there a little; giving us consolation by holding forth that which is to come, confirming our hope!