Picture it; a slim-fit white temple dress in the midst of a religious ceremony. Is it a wedding? It could be. Yet, temple dresses have their origins in Mormon and/or Jewish temples. In fact, this very style of dress could be used to meet multiple religious requirements and ceremonies in multiple religions. Take a look.
A Baptist's Baptism
Baptists are one (of a few) Protestant religion that does not baptize babies. More often than not, they baptize adults, and sometimes children or teens who protest their faith in God as real and true. If you ever want to be baptized as a Baptist, or make that conversion, a white temple dress is perfect, since Baptist ministers frequently have those being baptized wear white gowns or robes anyway.
Jewish Yom Kippur
White gowns are symbolically worn on Yom Kippur to represent the atonement for sin. Hasidic Jews may wear white gowns more frequently because white gowns hide ankles, knees, elbows, and wrists from view and white does not draw male attention because it is not a bright and forbidden color. It is highly unlikely that you will ever become a Hasidic Jew, but you can still show respect to their culture and their faith by wearing a white gown on Yom Kippur (if you enter a temple or celebrate with Jewish friends).
Mormon Tabernacle Services
Men and women of the Mormon faith are required to dress in a very specific fashion before they are allowed into the Holy Tabernacle. Women also have separate services and sit apart from men, much in the same way ancient Jewish religious ceremonies and weddings were celebrated. If you are Mormon, there are many lovely white temple dresses to choose from. If you are not Mormon, you will not be allowed in the Tabernacle anyway, so do not worry about it.
Lutheran Confirmation or Catholic Communion
In both these ceremonies, children receive sacraments or rights. The girls typically wear all white to resemble "little brides of Christ." If you convert to Lutheranism or Catholicism as an adult in order to marry someone who is Lutheran or Catholic, the ceremonies are the same and, as an adult female, you would still have to wear a white, reasonably modest dress to your ceremony. A handful of other Protestant religions that practice infant baptism like the Catholic church also practice confirmation and hold regular ceremonies for "graduates" of religion classes.