Mark 10:6-8: '"But at the beginning of creation God 'made them male and female.' For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh.' So they are no longer two, but one flesh."'
Qur'an 30:21: '"And of His signs is that He created for you mates from among yourselves, so that you may find tranquility in them; and He planted love and compassion between you."'
Many religions specify it must be a man and a woman - gay marriage is legal and accepted in many countries
Most people still use some element of religious ceremony in their marriages, showing that they are still relevant
"Til death do us part" - most marriages end within 5 years
Although many people get divorced, the added security of God involved in a marriage may make people work harder to preserve it
In Islam, you are technically allowed more than one wife - in many societies, this is illegal / seen as wrong
Although religious texts may say things that are old-fashioned or illegal in some countries, the religious leaders in those countries adapt their teachings to fit the society (e.g. most CoE churches allow gay marriage)
In some religions (e.g. Islam), the bride is "given away" by their father/guardian - many people would argue this treats the woman as an object
Many people now treat the more old-fashioned elements of religious marriage as a tradition rather than a serious thing (e.g. many women may want to be "given away" but know they are not an object)