Polygamy could be legalised in two decades, Pastor Mark Driscoll has warned. Soon, he says, many types of relationships will be deemed "worthy of qualifying as marriage".

Driscoll sets out his concerns in his latest Mark Driscoll Ministries newsletter.

He addresses a question from one of his viewers on whether polygamy should be embraced today, given that there are examples of it in the Old Testament. 

Driscoll notes that Isaac, Abraham's son with his wife Sarah, was the ancestor of the Jewish people while Ishmael, Abraham's son with his wife Hagar, gave rise to the Arab nations.

"And so a lot of the Jewish-Arab conflict today comes from poylgamy," he concludes. "One guy having two wives, through those two wives come two sons, from those two sons coming two lines."

Esau and Jacob were also polygamists. Driscoll says the Bible records lots of pain and conflict because of polygamy, for example where one wife is favoured over another and issues over who gets to inherit.

"When polygamy occurs the results are disastrous. They are painful," he says.

Driscoll asked his wife Grace her view and she agreed with him: that to any son-in-law, he would say he should love his daughter and "not pick up any additional wives".

Driscoll says that not far from his new Trinity church, which is in Scottsdale, Arizona, polygamy is still practised by some people. "It is an issue here," he says.

But the question is also timely because of the present debate throughout Western society about the definition of marriage.

"It was historically in the Western world, with very rare exceptions, one man one woman. Well we have now not just a man and a woman but a man and a man or a woman and a woman to be able to legally marriage [sic]. My question is, what is our definition of marriage culturally? It doesn't seem like we have one, and the result is it's open to discussion and debate.

"So my belief is it is entirely possible, if not probable, that you will see polygamy legalised in our lifetime as you now have people who are more gender fluid."

He said the argument will be made that it would allow people to express the "fullness" of their gender identity. Some will also argue that it will reduce divorce, he added, noting that some television shows are already showing polygamous families, with the effect that it could move towards becoming a cultural norm.

But Driscoll is in no doubt that it is sinful.

"I don't think it's wise, I don't think it's Godly, I don't think it's God's original intention or design." He added: "God's intent by creation and design is one man and one woman."

Driscoll, who has two teenage daughters, says: "The last thing I would want is my daughters being married to some dirty old man who had multiple wives and was constantly adding to his harem... It's not God's will or intent."