An important factor in choosing your music is the setting for your wedding ceremony. On the other hand, if your ceremony will be in a church or synagogue, or conducted by a clergy person at another location, you will probably need to stay within guidelines set by the clergy person or the church.
Most religious denominations consider a wedding ceremony to be a form of worship service.
Some will allow secular music while the guests are being seated, but not during the ceremony itself. Check with the church where your wedding will be held for its specific guidelines. Many churches will also allow a song that does not make specific reference to a deity, as long as it focuses on religious ideals and values relating to love and marriage, such as faithfulness and mutual support. A good starting point for selecting your ceremony music is to meet with the church organist or pianist. This person will probably be happy to play various pieces for you that can be used for the processionals and the recessional.