Why do Mormons wear Jesus jammies?

Answer 1

The temple garment you refer to is a quiet and personal reminder of sacred covenants that an individual has made with Christ. They represent a deep personal commitment to use every bit of heart, might, mind and strength one possesses to serve Jesus Christ in word, deed and thought.

However if it is the idea of a sacred garment of any kind that you have a problem with then you need look no further than the Old Testament for examples of God's followers being required to wear sacred and symbolic clothing. All of ancient Israel was required to wear some sort of symbolic clothing. Especially the priests. A description of the symbolic clothing the priests were supposed to wear anciently can be found in Exodus chapter 28.

Answer 2

I have been a member of the Church of Jesus Christ of Latter-day Saints (the "Mormon" church) for 23 years and have never heard the term "Jesus Jammies". Maybe you are referring to the Temple Garment?

Members of the Church who have chosen to participate in an Endowment ceremony in the Temple are obligated to wear the Temple Garment throughout their life. This garment serves as a reminder of the covenants that they have made in the Temple ceremony and also serves as a sort of priestly robe. Because Mormons have a lay ministry, those who serve in the Church do not wear special robes or priest collars as in other Christian churches. They do, however, wear the Temple Garment as a symbol of their authority to lead in the Church.

The Temple Garment is considered very sacred by those who wear it. They should not show it to other people, nor should they speak casually about it. It is supposed to be worn day and night below the persons regular clothing, just like underwear. (so, it isn't really like pajamas at all...)