A basic explanation of why we have temples was given by President Gordon B. Hinckley in "Why These Temples?" (2001). An excerpt follows:
Was there ever a man or woman who, in a time of quiet introspection, has not pondered the solemn mysteries of life?
Has he or she not asked, "Where did I come from? Why am I here? Where am I going? What is my relationship to my Maker? Will death rob me of the treasured associations of life? What of my family? Will there be another existence after this, and, if so, will we know one another there?"
The answers to these questions are not found in the wisdom of the world. They are found only in the revealed word of God. Temples of The Church of Jesus Christ of Latter-day Saints are sacred structures in which these and other eternal questions are answered. Each is dedicated as a house of the Lord, a place of holiness and peace shut apart from the world. There truths are taught and ordinances are performed that bring knowledge of things eternal and motivate the participants to live with an understanding of our divine inheritance as children of God and an awareness of our potential as eternal beings.
These buildings, different from the thousands of regular Church houses of worship scattered over the earth, are unique in purpose and function from all other religious edifices. It is not the size of these buildings or their architectural beauty that makes them so. It is the work that goes on within their walls.
The designation of certain buildings for special ordinances, as distinguished from regular places of worship, is not new. This was the practice in ancient Israel, where the people worshiped regularly in the synagogues. Their more sacred place was, first, the tabernacle in the wilderness with its Holy of Holies, and then a succession of temples, where special ordinances were performed and where only those who met the required qualifications could participate in these ordinances.
So it is today. Prior to the dedication of a temple, The Church of Jesus Christ of Latter-day Saints invites the public to go through the building and inspect its various facilities. But when it is dedicated it becomes the house of the Lord, vested with a character so sacred that only members of the Church in good standing are permitted to enter. It is not a matter of secrecy. It is a matter of sanctity.
The work that goes on in these buildings sets forth God's eternal purposes with reference to man--God's child and creation. For the most part, temple work is concerned with the family, with each of us as members of God's eternal family and with each of us as members of earthly families. It is concerned with the sanctity and eternal nature of the marriage covenant and family relationships.
For more information on temples, see the links in the panel to the left.