One of the primary ordinances in the Mormon temple is the endowment ceremony.  During this ceremony, members of the Church of Jesus Christ of Latter-day Saints come to the temple to make covenants with God.

What is a covenant?

mormon-temple-marriageLDS.org describes:

A covenant is a sacred agreement between God and a person or group of people. God sets specific conditions, and He promises to bless us as we obey those conditions.

When LDS members come to the temple for the endowment ceremony, it is to make those promises to God that we will follow His commandments.

Do all Mormons go through the endowment ceremony?

Typically, Mormon young men will go through the endowment ceremony before they are called to serve as Mormon missionaries around the ages of 19 to 26 years old.  Similarly, Mormon young women will participate in the endowment ceremony before they are called to serve as Mormon missionaries, or before they get married.

Is the endowment ceremony a one-time event for Mormons?

Yes and no.  The first time Mormons participate in the endowment ceremony, they are making those covenants with God for themselves.  Mormons can then return to participate in the endowment ceremony for and in behalf of their deceased ancestors.  Just as Mormons are baptized by proxy for their deceased ancestors, they also stand in for the endowment ceremony.

Mormons enjoy returning to participate in the endowment ceremony because it serves as a reminder of the covenants they have personally made with God and also because of the peace that temple worship provides.