Beliefs are either in accord with truth or not. There is no relativity of belief because there is no moral relativity in the cosmos. There is fixed moral truth just as there is fixed mathematical truth. Both find their source is Jesus Christ.
If there were no absolute moral truth you would have no real basis to be against anything you are against or for anything you are for. There would be no truly grounded moral argument against murder or government tyranny or theft. But because there is a God in heaven who established cosmic moral law, we have a firm foundation with which to oppose such violations of the moral law as I pointed out above.