There was a time when the biblical worldview was taken for granted, when historical facts, the laws of nature, logical ideas, divine revelation, and moral principles were all issues of truth. Call this time of openness to outside reality "premodern." The narrowing of the mind began in the 18th century when "modernists," giddy with the promise of science and the dream of Enlightenment progress, claimed that the only truths were those testable by scientific rationalism.
The modernist confidence in naturalistic reason is now passé; Christians can applaud that. But while many are taking advantage of the decline of modernism to rediscover biblical realism, the cultural mainstream has turned to postmodernism, a worldview that tries to do without truth altogether.
For postmodernists, truth is merely a "construction" by the culture or by the individual. We construct our beliefs, so that what is true for me may not be true for you. Truth, as they say, is relative. Morality depends on the individual's choice. Religion occupies a private corner of the brain, as a source of personal serenity, but not a set of truth claims about ultimate reality, much less a relationship with an external, demanding, sovereign God.
The rejection of truth in postmodernism means that attempts to persuade are construed as acts of oppressive power. Since everyone's beliefs have equal validity, "you don't have the right to impose your beliefs on anybody else." Logical contradictions are OK. The willingness to change one's story is a function of the ability to "reinvent" oneself.
In the postmodernist dismissal of truth, image is everything. The meaning of words is not fixed but a function of "interpretation," so that the speaker, listeners, and spin-doctors can construct their own meanings for them. What matters is not substance but projecting a positive image.