The covenants and ordinances of the Gospel of Jesus Christ are necessary for obtaining eternal life

Mosiah 18:9-11

9. Yea, and are willing to mourn with those that mourn; yea, and comfort those that stand in need of comfort, and to stand as witnesses of God at all times and in all things, and in all places that ye may be in, even until death, that ye may be redeemed of God, and be numbered with those of the first resurrection, that ye may have eternal life—
10. Now I say unto you, if this be the desire of your hearts, what have you against being baptized in the name of the Lord, as a witness before him that ye have entered into a covenant with him, that ye will serve him and keep his commandments, that he may pour out his Spirit more abundantly upon you?
11. And now when the people had heard these words, they clapped their hands for joy, and exclaimed: This is the desire of our hearts.

Exodus 19:3-6

3. And Moses went up unto God, and the Lord called unto him out of the mountain, saying, Thus shalt thou say to the house of Jacob, and tell the children of Israel;
4. Ye have seen what I did unto the Egyptians, and how I bare you on eagles’ wings, and brought you unto myself.
5. Now therefore, if ye will obey my voice indeed, and keep my covenant, then ye shall be a peculiar treasure unto me above all people: for all the earth is mine:
6. And ye shall be unto me a kingdom of priests, and an holy nation. These are the words which thou shalt speak unto the children of Israel.

D&C 84:19-22

19. 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.
20. Therefore, in the ordinances thereof, the power of godliness is manifest.
21. And without the ordinances thereof, and the authority of the priesthood, the power of godliness is not manifest unto men in the flesh;
22. For without this no man can see the face of God, even the Father, and live.

D&C 84:33-39

33. For whoso is faithful unto the obtaining these two priesthoods of which I have spoken, and the magnifying their calling, are sanctified by the Spirit unto the renewing of their bodies.
34. They become the sons of Moses and of Aaron and the seed of Abraham, and the church and kingdom, and the elect of God.
35. And also all they who receive this priesthood receive me, saith the Lord;
36. For he that receiveth my servants receiveth me;
37. And he that receiveth me receiveth my Father;
38. And he that receiveth my Father receiveth my Father’s kingdom; therefore all that my Father hath shall be given unto him.
39. And this is according to the oath and covenant which belongeth to the priesthood.

D&C 109: 1, 14-15, 21-24

1. Thanks be to thy name, O Lord God of Israel, who keepest covenant and showest mercy unto thy servants who walk uprightly before thee, with all their hearts—

14. And do thou grant, Holy Father, that all those who shall worship in this house may be taught words of wisdom out of the best books, and that they may seek learning even by study, and also by faith, as thou hast said;
15. And that they may grow up in thee, and receive a fulness of the Holy Ghost, and be organized according to thy laws, and be prepared to obtain every needful thing;

21. And when thy people transgress, any of them, they may speedily repent and return unto thee, and find favor in thy sight, and be restored to the blessings which thou hast ordained to be poured out upon those who shall reverence thee in thy house.
22. And we ask thee, Holy Father, that thy servants may go forth from this house armed with thy power, and that thy name may be upon them, and thy glory be round about them, and thine angels have charge over them;
23. And from this place they may bear exceedingly great and glorious tidings, in truth, unto the ends of the earth, that they may know that this is thy work, and that thou hast put forth thy hand, to fulfil that which thou hast spoken by the mouths of the prophets, concerning the last days.
24. We ask thee, Holy Father, to establish the people that shall worship, and honorably hold a name and standing in this thy house, to all generations and for eternity;

Abraham 2:8-11

8. My name is Jehovah, and I know the end from the beginning; therefore my hand shall be over thee.
9. And I will make of thee a great nation, and I will bless thee above measure, and make thy name great among all nations, and thou shalt be a blessing unto thy seed after thee, that in their hands they shall bear this ministry and Priesthood unto all nations;
10. And I will bless them through thy name; for as many as receive this Gospel shall be called after thy name, and shall be accounted thy seed, and shall rise up and bless thee, as their father;
11. And I will bless them that bless thee, and curse them that curse thee; and in thee (that is, in thy Priesthood) and in thy seed (that is, thy Priesthood), for I give unto thee a promise that this right shall continue in thee, and in thy seed after thee (that is to say, the literal seed, or the seed of the body) shall all the families of the earth be blessed, even with the blessings of the Gospel, which are the blessings of salvation, even of life eternal.

Entering the new and everlasting covenant of marriage is necessary for eternal life.

D&C 131:1-4

1. In the celestial glory there are three heavens or degrees;
2. And in order to obtain the highest, a man must enter into this border of the priesthood [meaning the new and everlasting covenant of marriage];
3. And if he does not, he cannot obtain it.
4. He may enter into the other, but that is the end of his kingdom; he cannot have an increase.

D&C 132:15-17; 19-20

15. Therefore, if a man marry him a wife in the world, and he marry her not by me nor by my word, and he covenant with her so long as he is in the world and she with him, their covenant and marriage are not of force when they are dead, and when they are out of the world; therefore, they are not bound by any law when they are out of the world.
16. Therefore, when they are out of the world they neither marry nor are given in marriage; but are appointed angels in heaven, which angels are ministering servants, to minister for those who are worthy of a far more, and an exceeding, and an eternal weight of glory.
17. For these angels did not abide my law; therefore, they cannot be enlarged, but remain separately and singly, without exaltation, in their saved condition, to all eternity; and from henceforth are not gods, but are angels of God forever and ever.

19. And again, verily I say unto you, if a man marry  a wife by my word, which is my law, and by the new and everlasting covenant, and it is sealed unto them by the Holy Spirit of promise, by him who is anointed, unto whom I have appointed this power and the keys of this priesthood; and it shall be said unto them—Ye shall come forth in the first resurrection; and if it be after the first resurrection, in the next resurrection; and shall inherit thrones, kingdoms, principalities, and powers, dominions, all heights and depths—then shall it be written in the Lamb’s Book of Life . . . in time, and through all eternity; and shall be of full force when they are out of the world; and they shall pass by the angels, and the gods, which are set there, to their exaltation and glory in all things, as hath been sealed upon their heads, which glory shall be a fulness and a continuation of the seeds forever and ever.
20. Then shall they be gods, because they have no end; therefore shall they be from everlasting to everlasting, because they continue; then shall they be above all, because all things are subject unto them. Then shall they be gods, because they have all power, and the angels are subject unto them.

Sacred ordinances performed in holy temples make it possible for deceased family members to receive the blessings of salvation

D&C 2:1-3

1. Behold, I will reveal unto you the Priesthood, by the hand of Elijah the prophet, before the coming of the great and dreadful day of the Lord.
2. And he shall plant in the hearts of the children the promises made to the fathers, and the hearts of the children shall turn to their fathers.
3. If it were not so, the whole earth would be utterly wasted at his coming.

D&C 128:18,24

18. I might have rendered a plainer translation to this, but it is sufficiently plain to suit my purpose as it stands. It is sufficient to know, in this case, that the earth will be smitten with a curse unless there is a welding link of some kind or other between the fathers and the children, upon some subject or other—and behold what is that subject? It is the baptism for the dead. For we without them cannot be made perfect; neither can they without us be made perfect. Neither can they nor we be made perfect without those who have died in the gospel also; 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.

24. Behold, the great day of the Lord is at hand; and who can abide the day of his coming, and who can stand when he appeareth? For he is like a refiner’s fire, and like fuller’s soap; and he shall sit as a refiner and purifier of silver, and he shall purify the sons of Levi, and purge them as gold and silver, that they may offer unto the Lord an offering in righteousness. Let us, therefore, as a church and a people, and as Latter-day Saints, offer unto the Lord an offering in righteousness; and let us present in his holy temple, when it is finished, a book containing the records of our dead, which shall be worthy of all acceptation.

JSH 1: 72-74

72. The messenger who visited us on this occasion and conferred this Priesthood upon us, said that his name was John, the same that is called John the Baptist in the New Testament, and that he acted under the direction of Peter, James and John, who held the keys of the Priesthood of Melchizedek, which Priesthood, he said, would in due time be conferred on us, and that I should be called the first Elder of the Church, and he (Oliver Cowdery) the second. It was on the fifteenth day of May, 1829, that we were ordained under the hand of this messenger, and baptized.
73. Immediately on our coming up out of the water after we had been baptized, we experienced great and glorious blessings from our Heavenly Father. No sooner had I baptized Oliver Cowdery, than the Holy Ghost fell upon him, and he stood up and prophesied many things which should shortly come to pass. And again, so soon as I had been baptized by him, I also had the spirit of prophecy, when, standing up, I prophesied concerning the rise of this Church, and many other things connected with the Church, and this generation of the children of men. We were filled with the Holy Ghost, and rejoiced in the God of our salvation.
74. Our minds being now enlightened, we began to have the scriptures laid open to our understandings, and the true meaning and intention of their more mysterious passages revealed unto us in a manner which we never could attain to previously, nor ever before had thought of. In the meantime we were forced to keep secret the circumstances of having received the Priesthood and our having been baptized, owing to a spirit of persecution which had already manifested itself in the neighborhood.