Giving him the benefit of the doubt, as a former pastor he could be trying to say that it being a Biblical issue ends the debate, since the Biblical is infinitely superior to the political. Therefore, since the Bible prescribes marriage as exclusively between one man and one woman, that should end the political discussion. If ours was still a Christian nation, of course.
The Bible also prescribes pork as an unclean meat that is forbidden to eat and does not allow shaving, stating "do not trim off the hair on your temples or trim your beards".
If your ONLY argument against gay marriage is "the Bible says its wrong", that will be the response to the discussion.