The Ordinances of the Temple were instituted by the Lord in the New Testament, as they were originally in the days of Adam. Then again, they were Restored in our day through the Prophet Joseph Smith. These ordinances prepare us to be in the presence of the Lord, both on earth and in the life to come.
About the Endowment, Brigham Young has said, “Your endowment is, to receive all those ordinances in the house of the Lord, which are necessary for you, after you have departed this life, to enable you to walk back to the presence of the Father, … and gain your eternal exaltation.” Brigham Young in Discourses of Brigham Young, sel. John A. Widtsoe (1941), 416.
The Endowment is spoken of in the New Testament, where the Savior, after he was resurrected and before sending the apostles out to teach, said to "tarry ye at Jerusalem, until ye be endued with power from on high." (Luke 24:49 https://www.lds.org/scriptures/nt/luke/24.49 )
And there are the sealing ordinances there, too. After Peter declared that Jesus was the Christ, The Savior said to him "And I will give unto thee the keys of the kingdom of heaven: and whatsoever thou shalt bind on earth shall be bound in heaven: and whatsoever thou shalt loose on earth shall be loosed in heaven." (Matthew 16:19 https://www.lds.org/scriptures/nt/matt/16.19 )
That is what happens in Temples. This power to bind on earth and in heaven was restored to the prophet Joseph Smith and recorded in the Doctrine and covenants multiple times (D&C 127:7, D&C 124:93, D&C 132:46, D&C 128).
Additionally, baptisms for the Dead were spoken by Paul, who said "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?" (1 Corinthians 15:29 https://www.lds.org/scriptures/nt/1-cor/15.29). In this modern era, this ordinance is done as it was done in the New Testament church, so that our ancestors who never heard the gospel, or those who never heard of Christ can return to the presence of the Lord. For the Savior said all must be baptized in John 3:5, when he said "except a man be born of water and of the spirit, he cannot enter the kingdom of heaven." (https://www.lds.org/scriptures/nt/john/3.5 ).
We are told in modern revelation that these same ordinances were given to Adam, and later to Abraham. For more on this topic, see the search page https://www.lds.org/search?lang=eng&query=temple+ordinances+adam
Because of the miracle of the Restoration of the Gospel, the sacred temple ordinances the Savior established in New Testament times, and back in the time of Adam, have been restored to this earth to bless our Father in Heaven's children. With the miracle of temple work, all of Father in Heaven's children who have ever lived on the earth, and who would have accepted it if they were alive, will be able to have the opportunity to accept or reject those blessings, and inherit all that our Father in Heaven has. And these blessings were spoken of in the Bible.
And for us, when we go to the temple to do the work of our dead, we are able to feel of God's presence. The Doctrine and Covenants states "my glory shall rest upon it; Yea, and my presence shall be there, for I will come into it., and all the pure in heart shall see God" (D & C 97:15-16 http://bit.ly/14GTNd6 )
The spirit in temples is stronger than in any other place on earth. While there we can perform sacred ordinances for our ancestors that are necessary for them to return to the presence of God. Find out more about temples by going to http://www.lds.org/church/temples
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