Moral relativism, the belief that all moral decisions and evaluations are dependent on the surrounding society and culture, is simply not true. If something is wrong, it is wrong for all people at all times.
Take slavery for example: we modern Christians know slavery is wrong, and that slave-holders are immoral, but 200 years ago people thought slavery was perfectly moral. If the moral relativists are right, those slave-holders weren't immoral, they were just following the morality of their times. But, since we modern Christians know that slavery was always wrong, there must be an absolute morality as given by the Bible.
Step Seven