Truth is an inherently “Christian” (perhaps more appropriately, “theist”) position. Truth assumes absolutes. Absolutes assume an absolute. There is only one absolute: God. God defines what is absolute, and, despite what our atheistic culture would have us think about the “relativistic nature of reality”, reality is absolute.
Truth is absolute because God is absolute and because of this whatever God says is true. Truth is important and when we give it up we cannot function in a Christ-like manner. Those who have “crept in unnoticed” do not present truth. Truth is important because it is what God says. When God speaks we are commanded to listen.