“Truth” – aletheia – is one of the words which, although already richly diverse in its classical usage, took on a whole new dimension in the New Testament. Jesus’ use of the term in one of his “I AM” statements – Jn.14:6 — is as unique in literature as he himself is unique among people. So as we pursue Pilate’s (probably cynical) question, “What is truth?” (Jn.18:38), it must be with the realization that, ever since Jesus walked the earth, “truth” is no longer only a “what?”, but a “who?”, and one’s answer to that question determines the entire direction of his life.
The classical writers parallel many modern understandings of “truth”:
— honesty; the opposite of lying, falsehood, or pretense
— genuine, as opposed to artificial; correct, as opposed to mistaken
— frankness or candidness in persons, as opposed to hypocrisy
–reality, as opposed to mere imitation, or, as in Plato, the “form” rather than a “shadow”
These are reflected in some of the New Testament uses of “truth” as well: in the idea of being “without deception” (Mt.22:16, Mk.12:14, Jn.4:23-24, Jn.8:40-46), or specifically “not lying or pretending” (Lk.4:25, 22:59, Mk.5:33, 12:32, Jn16:7, Rom.9:1, II Cor.7:14, 12:6, Phil.1:18,) among others.
But in the New Testament, as Bauer’s lexicon notes, “Truth has a strongly practical side, which expresses itself in [behavior].” Truth is something you DO, not a theoretical statement of intellectual conclusions. John, in particular, writes of “obeying the truth” or “walking in the truth” (Jn.3:31, I Jn.1:6, II Jn 4, III Jn.3-4), as do Paul (Rom.2:8, II Cor.3:8, Gal.2:14, 3:1, 5:7), James (5:19), and Peter (I Pet.1:22). This list can be expanded even more when one keeps in mind that pisteuo, traditionally translated “believe”, actually means “be/become faithful to” (see Word Study #1).
When the New Testament writers speak of “becoming faithful to the truth,”(traditional versions say “believing”) (I Thess.2:13, I Tim.4:3, II Tim.3:7), or “knowing (Col.1:6) the truth” (Paul uses epiginosko here – a strongly experiential form of “knowing”(as does the writer to the Hebrews in 10:26)—they are not referring to any sort of intellectual assent to a list of propositions, but to a chosen way of life!
I Jn.3:18 is especially interesting in this regard, as he admonishes his readers, “Dear children, let’s don’t love in theory [word] or in talk, but in action and truth!”
Also of interest are the instances where “truth” is paired with a noun in the genitive case. Remember that although the most common use of the genitive is to indicate possession, it may also refer to a source (“coming from”) or the content (“made of”, “consisting of”). Paul speaks of “the truth of Christ” (II Cor.11:10) or “of God” (Rom.1:25, 3:7), very likely an indication of source, and “of the Gospel (Gal.2:5) most likely content. Turning the cases around, John refers to the “spirit of truth” (Jn.15:26, 16:3, I Jn.4:6), and Paul to “the word of truth” (IICor.6:7, Eph.1:13, Col.1:5, II Tim.2:15) , more likely to be a possessive genitive. These come into sharper focus in the light of Jesus’ statements:
–“I AM …the truth” (Jn.14:6)
— “Thy word is truth” (Jn.17:17) (Remember that John had introduced Jesus himself as “the Word” – Jn.1:1)
— and John’s reminder, “The spirit is truth” (I Jn.5:6).
These three are the only references that seem to make any effort to actually define the term.
Truth is also presented as an active force in human affairs:
–Jesus’ statement, “You shall know the truth, and the truth shall make you free” (Jn.8:32)
–Jesus’ prayer, “Set them apart [make them holy] by [in] the truth” (Jn.17:17)
–James 1:18, where it is represented to be the agent of our birth into the family of God.
None of this should be seen as an attempt to minimize the understanding of “truth” as the absolute honesty and transparency, in both life and speech, expected of all God’s people. That is basic to all the citations here.
Warnings about opposition to the truth, or refusal to be obedient to it/him, (Rom.1:18, 1:25, 2:8; Gal.2:14, 3:1, 5:7; II Thess.2:10, 2:12; I Tim.6:5, II Tim.2:18, 3:8, 4:4, Tit.1:14, I Jn.1:6, 1:8,2:4) are in no case concerned about the intricate details debated during centuries of theological speculation by hierarchical councils of various descriptions. They are concerned with the behavior of those claiming to represent the Lord Jesus.
The same One who explained to Pilate that the purpose of his coming was to “bear witness to the Truth” (Jn.18:37), had earlier proclaimed himself to be the very personification of Truth! (14:6). What clearer synopsis, or identification, could there be, than “Everyone who is from [or, belongs to] the truth, listens to [obeys] my voice” (18:37)? The Way, the Truth, and the Life, are all about the Lord Jesus!
They all simply refer us back to the same question invoked in several of our earlier studies:
Who’s calling the shots?
Who is in charge?
Who is your King?
The Pioneers' New Testament 
And as you have pointed out so many times before, Mom, “Who’s your king” is so much more than “who’s your savior?”
In this light, you might enjoy a post my friend Mason just put up, in which he tries to summarize “the Gospel” in a different framework than the one he’s been taught all his life. I think he’s on to something.
Correct. I looked at that post, and basically agree. Citizens of the Kingdom posits a similar theme.