Here's an excerpt from an article:
"A different view is held by Christianity: there is an absolute standard of reference and against it everyone and everything is measured. This ultimate and absolute standard is God. He has sufficiently revealed Himself in the Bible where we learn that He is the Truth and speaks truthfully. We read, for instance, that: "God is not a man, that He should lie, nor a son of man, that He should change His mind..." (Numbers 23:19). And elsewhere, it says it is "... impossible for God to lie..." (Hebrews 6:18, cf. Titus 1:2). This means that even if He wanted to, God cannot lie. Jesus in John 14:6 did not say that He is just another carrier of truth; He said that He is Truth itself. This means that for God, truth and reality are fixed.
He does not say this today and then unsays it tomorrow. He does not give a commandment and then tells man, "Just apply it as you see fit." His Word is final and His standards absolute. Psalm 119:89 says: "Your word, O Lord, is eternal; it stands firm in the heavens."
"What, then, are the differences between relative truth and absolute truth?
First, while absolute Truth is independent and immutable (unchanging), relative Truth is dependent on the situation and the individual, and changes with circumstances. This makes it extremely difficult to depend on because it is dependent itself.
Second, while absolute Truth meets the logical tests of systematic consistency, experiential relevance and empirical adequacy, relative Truth is self-stultifying. By this I mean that absolute Truth stands the test of Non-contradiction but relative Truth does not and cannot - it contradicts itself and so destroys itself. One cannot even make the statement "All truth is relative" without contradicting himself. Why? Because it is an absolute statement declaring the non-existence of absolutes like itself. It is like the ancient Hindu saying, "He who speaks does not know and he who knows does not speak." And yet since the one who posited the statement spoke, the statement goes round his neck and strangles him, because if he knew, he would not have spoken. He "does not know" because he spoke to tell us that. And thus, the denial of absolutes is self-destructing."
The whole article can be found here:
http://www.wtmkenya.org/apologetics/ap7.htm