My own search for Truth began in the classroom. We studied subjects like physics and chemistry, maths and history, and I thought we were learning truths.
Then when I got older I started reading philosophy. I read about a guy called Socrates who was one of the cleverest men of his day. He lived in Athens during the 5th century, when the Greek state was at the zenith of its power and influence. Now this clever guy devoted his life to the search for truth. We are fortunate to have catalogues of his conversations with the hoi polloi of the times, men with influence and power. These were written up by Plato, also a philosopher. While we have to be wary when reading about someone else's beliefs through a third party, we can still get a fairly accurate view of Socrates' methods. The type of debate he employed was called "dialectic", a series of simple questions and answers which he hoped ultimately would lead to a true conclusion. Even this clever man could only say at the end of his life, before he took the hemlock that killed him, that the only thing he knew for sure was the he knew nothing. He realised he could not avoid false premises. A false premise makes the rest of the argument false too.
When we ask "What is Truth?" we are already assuming that we know a concept called truth exists and we have a very good idea what we think it means. What we are really asking is "Can we come up with a believable argument that supports what we already believe?" The answer clearly, a circle, must be no. So modern philosophy has become more of an exercise in semantics and word play, less a search for universal truth.
Socrates (and Plato) had enough trouble trying to define simple objects such as "Table" and "Chair", so when it came to answering more complex questions such as the nature of "Goodness" the game became impossible. Plato's solution was to invent a separate plane of existence for these indefinable ideals. This was his Theory of Forms, where every "concept" exists in its perfect state completely away from us and from where we can draw only imperfect copies. In other words, we see "Truth" only through the prism of our existence, always distorted by our own perceptions.
Yes, there has been a lot of work done on this since Plato, but the basic concept, that truth is unobtainable in its purest form, has not been improved upon. Truth at best, in human terms, can only ever be what the majority agree it is, which is unfair to the minority who may have their own ideas - after all, if someone is convinced they see pink elephants, who are we to argue?
Fortunately it IS possible to come to a close approximation of our external reality through simple observation; that's what science is, an attempt to regularise our perceptions to the point where we can control and manipulate the reality around us. But even with the extraordinary leaps in knowledge of the last hundred years, scientists are still just scratching the surface of what is really going on. There are a mass of unknowables that form an iceberg sunk beneath our visibility.
Enter religious faith. The importance of faith is that it is belief in things that are invisible. This may sound like fairyland, but we have an important testament (two in fact, and Old and a New) in the Bible which explains everything. How do we know the Bible is true? Because, put quite simply, it is too vast, too complicated, and makes too much sense, to be anything else. The Bible is a convincing mixture of absolute fact (the long lists of generations, for example, name by name which could easily have been contested but never were) and revealed prophecy. The facts speak for themselves; the prophecy requires faith, but even the prophecies, right down to the life of Jesus and the formation of the first church, contain so much self-affirmation, witness and testimony that even the most ardent cynic would be hard put to form a serious argument against them.
So when Jesus says, as he does so often, "I tell you the truth..." we are compelled to believe him. If Jesus had lied in front of so many people, he would have been found out and his credibility would have collapsed. The crucifixion would not have been necessary. He would simply have been turfed out as a crazy man.
Through our faith, relative concepts are turned into absolute truth. Absolute truth is truth which does not vary in any circumstances and never needs to be questioned. If Socrates had been alive in Jesus' day, he would have dispensed with the hemlock and embraced Him as his saviour. Exactly as we should today.