The certainty of a proposition is the property that it cannot fail to be true. The truth of Christianity is not simply an autobiographical quality, telling us something about its acceptability to this or that individual person. The apologist defends the objective truth of the faith. Another low road which some professing Christians take in response to unbelieving objections to the faith is the road of relativism. This is closely allied with subjectivism in many cases but constitutes a distinct error of its own.
Relativism is either hypocritical or self-contradictory.
Sometimes people play at relativism but do not really mean it. Christianity does not claim to be relatively true, but absolutely and universally so. Furthermore, as a religious system it claims to be exclusively true . This is naturally quite offensive in a pluralistic, democratic age. But that is not the point.