As Christianity was adopted into the ancient Celtic lands, many couples chose to have a combined wedding of their Christian beliefs with some of the Handfasting traditions.
There are many rituals that are part of the ancient Handfasting Ceremony, but one that I've read about often is the minister ties a strip of cloth around the couple's hands. If it is a temporary agreement, it will be loosely tied. If they have a permanent agreement, it will be tied tighter, thus the expression, "tie the knot". The couple will then kiss each other as their first gift to each other. The bride does not necessarily wear a traditional white bridal gown.