Covenants: Preparing to enter the house of the Lord

Whenever the Lord has had a people on the earth who will obey His word, they have been commanded to build temples in which the ordinances of the gospel and other spiritual manifestations that pertain to exaltation and eternal life may be administered. In cases of extreme poverty or emergency, these ordinances may sometimes be done on a mountaintop (see D&C 124:37–55). This may be the case with Mount Sinai and the Mount of Transfiguration. The tabernacle erected by Moses was a type of portable temple, since the Israelites were traveling in the wilderness. (LDS Bible Dictionary)
     And thou shalt bring Aaron and his sons unto the door of the tabernacle of congregation and wash them with water, And thou shalt put upon Aaron the holy garments, and anoint him and sanctify him...  (Exodus 40:12-13)
     Since the temple built by Solomon in all its grandeur and glory, there were no Houses of the Lord until the Lord commanded Joseph Smith, in the 1800's, to build a house for Him. The Lord expects anyone entering His presence to be cleansed. No unclean thing can dwell with God. (1 Ne 10:21) Once we have chosen to covenant, as evidenced by being baptized, with God, it is not a "done deal" that no more is expected of us until we die and are resurrected. We have an opportunity to continue to learn and progress and even enter the Lord's presence. 
Temples are literally houses of the Lord. They are holy places of worship where individuals make sacred covenants with God. Because making covenants with God is such a solemn responsibility, individuals cannot enter the temple to receive their endowments or be sealed in marriage for eternity until they have fully prepared themselves and been members of the Church for at least a year. (LDS.Org, topic "Temples")
     All of God's children will continue to progress through eternity and we will retain everything we gain in the way of learning truth and God's principles during our mortal life. Making covenants is a way of showing God our sincere desire to obey His and strive to be like Him and His Son. I am so grateful that my Heavenly Father believes in me enough to trust me with the light He wants to share with all of His children as soon as they are willing. I am far from being like my Savior but I believe that His admonitions to follow Him mean that I can.