Jesus said to Pilate, "... the reason I was born and came into the world is to testify to the truth.
Everyone on the side of truth listens to me.” Pilate asked Jesus, "What is truth?" - John 18:37-38 NIV
Still a good question.
Absolute truth - Do we know what it is?
Historic question in philosophy--epistemological question. A good portion of the history of philosophy devotes itself to this question. How can we see things but as men, and certainly not as God sees them. And since things consist of smaller things, they can be rearranged, questioning what they are in their various forms.
And since our eyes see things, perhaps our eyes are interpreting things differently than how others with different senses perceive them? Well, we can't be silly and must restrict ourselves to human experience, like it or not. Things are as we all in common experience them. We know those things with absolute truth.
But what makes things absolutely true, and not a deception? It is when God the Creator reveals to us the truth. Since we are defective we may mistake some experiences as from God when they are not. So we have to recognize we're fallible.
But certain truths from God about our Salvation are infallible because God has made doubly sure, through a variety of sources, that we can be assured of certain things. We have Scriptures. We have history. We have fellow Christians with their common experiences, common revelations, and common truths.
The new nature we receive from Christ when we adopt him as our life is absolute truth. Nominal Christianity does not fully perceive this, though they do experience the power of Christ. They know something happens from God. But they are not completely changed. They deny a new nature is lasting and real. True born again Christians know differently.
There are many truths that lead up to this conclusion. I don't hope to cover any but a minimal amount here.