Colossians 3:18 - 4:1
ESV - 18 Wives, submit to your husbands, as is fitting in the Lord. 19 Husbands, love your wives, and do not be harsh with them.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
My sister didn't see the need to have anyone officiate at her "wedding"; after all they were both "Christians" and were "in love" and they knew they would be in love until their dying day, so they threw a big party and announced that they were married!
About five years later her "spouse" died. After the funeral she returned to the home they shared and that she had purchased a number of items for. A few days later she gets a letter from an attorney for the children of her now deceased "husband's" first wife stating she has 30 days to vacate the house. It turns out they weren't legally married, they were just living together. Consequently she got absolutely nothing from his estate.
Now had they been married, and even though her husband had left her nothing in his will, she still would be entitled to a certain amount of the estate under South Carolina's "elective share" laws. As it is she was left homeless and had to move into a hotel until she could get things sorted out.