The ritual is conducted with the wedding party nude, symbolizing that they have noting to hide from one another or the witnesses to the marriage.
At the end of the ceremony, the couple consummates their marriage... immediately. Right on/by the altar. This act shows the observers that the couple (or female) belongs to each other (or the male) and that no observers may try and take her.
Traditionally, the Best Man and Maid of Honor also have a go at each other, but on their own time.