Why do men Mormon wear such under garments?

Most adult men and women in the Church of Jesus Christ of Latter-day Saints (the "Mormon" church) choose to participate in a sacred Temple ceremony called the "Endowment". The Endowment ceremony bears some similarity to the ceremonies found in Exodus 28 and 38 and Leviticus 6 and 16, which involve the putting on of linen breeches and other sacred clothing. In this ceremony, participants make sacred covenants (promises) with God, and are given a sacred garment as a symbol and reminder of these covenants. Those who participate in the ceremony are obligated to wear the garment under their clothing at all times (except bathing, swimming, etc) as a tangible personal reminder and witness of these promises they have made. This is similar to a married person wearing a wedding ring or a baptized Christian wearing a cross necklace - it is a personal symbol of the commitment or promise they have made.
Since Mormons have a lay clergy, the garment also serves as a sort of priests robe, symbolizing that the person is eligible for leadership positions in the Church. This is like an ordained pastor, priest, or minister wearing a special robe or collar to signify their position. The garment also encourages modesty in dress, as it is not supposed to be exposed to the view of others.
The garment essentially looks like typical white t-shirt and white boxer shorts or boxer briefs. There are special styles designed for men and women, (the women's styles have more feminine touches but still cover the thighs, torso, and shoulders just like the men) but all are white and come in a variety of fabrics.
Most adult men and women in the Church of Jesus Christ of Latter-day Saints (the "Mormon" church) choose to participate in a sacred Temple ceremony called the "Endowment". The Endowment ceremony bears some similarity to the ceremonies found in Exodus 28 and 38 and Leviticus 6 and 16, which involve the putting on of linen breeches and other sacred clothing. In this ceremony, participants make sacred covenants (promises) with God, and are given a sacred garment as a symbol and reminder of these covenants. Those who participate in the ceremony are obligated to wear the garment under their clothing at all times (except bathing, swimming, etc) as a tangible personal reminder and witness of these promises they have made. This is similar to a married person wearing a wedding ring or a baptized Christian wearing a cross necklace - it is a personal symbol of the commitment or promise they have made.
Since Mormons have a lay clergy, the garment also serves as a sort of priests robe, symbolizing that the person is eligible for leadership positions in the Church. This is like an ordained pastor, priest, or minister wearing a special robe or collar to signify their position. The garment also encourages modesty in dress, as it is not supposed to be exposed to the view of others.
The garment essentially looks like typical white t-shirt and white boxer shorts or boxer briefs. There are special styles designed for men and women, (the women's styles have more feminine touches but still cover the thighs, torso, and shoulders just like the men) but all are white and come in a variety of fabrics.