Because only Christians can understand the meaning of swearing to God in church.
Getting married in church is unintentional and sacred, and now many wedding companies follow suit.
However, if a wedding is to be held in a church, it is assumed that this new family will be dominated by Jesus Christ; Is the head of this family, (of course, the household registration book may be the name of the man or woman) is the helmsman in charge of the direction of this family.
Even if the unbeliever holds a wedding in a church, it shows that he is willing to obey God's sovereignty in this family. At the same time, it is also to announce this important decision to all relatives and friends.
It can be said that the protagonist of the church wedding is not the bride and groom, but God, our savior Jesus Christ.