What is meant by Moses 1:39? I understand that immortality has already been fulfilled by the Savior but what is meant by Eternal Life?
1 Nephi 9:6 says that God has the power to fulfill all of his words.
All men will be baptized and have eternal endowments performed and the process of teaching the gospel continues after this life. None can inherit Eternal life but the clean and pure. Maybe what I am getting at is: could this process of development even take eternities for some?
In the Pearl of Great Price we are instructed, as you have pointed out (Moses 1:39), “For behold, this is my work and my glory– to bring to pass the immortality and eternal life of man.” The Lord’s work regarding our immortality has already been fulfilled when the Lord was resurrected, and thus proclaimed in scripture via prophecy, “therefore the grave hath no victory, and the sting of death is swallowed up in Christ.” (Mosiah 16:8)
The Book of Mormon scripture mentioned highlights first the knowledge of our Lord, and that in light of this knowledge the Lord is able to prepare a way to accomplish all his works and to fulfill all his words (promises/covenants). This is true, otherwise God would be a liar — ceasing then to be God.
Part of his work and glory, intelligence shared, is the work that is accomplished in our temples. A way prepared that all of the sons and daughters of God will have the opportunity to accept or reject intelligence, light and truth. A Book of Mormon prophet provided further insight regarding the choice we have to choose liberty, through our great mediator, or to choose captivity via the devil. If we choose captivity, we are thus informed that there is an eternal punishment which is affixed. (Alma 42:16)
As you are familiar with, we recognize upon final judgement we will receive our reward: Telestial, Terrestrial, or Celestial. Each Kingdom is governed by eternal laws. Those that are received into a Telestial state will be able to progress according to the laws of a Telestial state, and so on with a Terrestrial state.
As pertaining to Celestial laws, and those who receive exaltation, we will receive all the Father hath according to covenant. Thus, answering your last question Elder Joseph Fielding Smith offered this counsel,
“Salvation does not come all at once; we are commanded to be perfect even as our Father in heaven is perfect. It will take us ages to accomplish this end, for there will be greater progress beyond the grave, and it will be there that the faithful will overcome all things, and receive all things, and receive all things, even the fulness of the Father’s glory.
“I believe the Lord meant just what he said: that we should be perfect, as our Father in heaven is perfect. That will not come all at once, but line upon line, and precept upon precept, example upon example, and even then not as long as we live in this mortal life, for we will have to go even beyond the grave before we reach that perfection and shall be like God.”
Our mortality is our time to prepare to meet God. This is our time to do all in our power to receive eternal life via the great mediator, Jesus Christ. Upon final judgement, should we have honored our Father in heaven we will receive all that He hath and continue, beyond the grave, toward perfection until we have become like Him.