Because and through the great commission we are called to make disciples in a world influenced by the philosophy of postmodernism. Postmodernism to be brief, is a development in the late twentieth century critical, literary, and performance movement that reacts to modern art and literature; postmodernists suggest that truth is no longer verifiable, and that new art forms are best created by freely mixing previous styles and themes. Postmodernism holds that we all create our own reality. God tends to be ignored. Should he (she, it?) exist, he certainly has nothing to say about what we should believe or how we should behave.
This is our challenge in the present age! We are all learning together on this issue. If you are new to it, do not feel uncomfortable. But do feel the need to get the kind of training you need to combat this view. One of the problem are: postmodernism can be hard to define. It is easier to combat this view once you get a working definition for it.