The truth can simply be described as a summary of a Godly life. It is not the world's definition of "intellectual purity of understanding" but rather the Biblical definition of "righteous way of life."
"And that ye put on the new man, which after God is created in righteousness and true holiness." (Eph. 4:24)
"Seeing ye have purified your souls in obeying the truth through the Spirit unto unfeigned love of the brethren, see that ye love one another with a pure heart fervently..." (1 Pet. 1:22)
"If we say that we have fellowship with him, and walk in darkness, we lie, and do not the truth." (1 Jn. 1:6)
"But when I saw that they walked not uprightly according to the truth of the gospel, I said unto Peter before them all, If thou, being a Jew, livest after the manner of Gentiles, and not as do the Jews, why compellest thou the Gentiles to live as do the Jews?" (Gal. 2:14)
The Bible itself is indeed truth because it tells of Godly living, it sets laws for Godly living. The Bible is the very book in which we find the laws of truth, the book where the characteristics of Godly living are laid out for us. It lays out the boundary between good and evil, truth and sin. It is God's living word, the Word that leads us in truth and righteousness.
"For the hope which is laid up for you in heaven, whereof ye heard before in the word of the truth of the gospel..." (Col. 1:5)
"To whom we gave place by subjection, no, not for an hour; that the truth of the gospel might continue with you." (Gal. 2:5)
"In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise..." (Eph. 1:13)
Jesus Christ is truth because He lived the life of truth. He never sinned, never violated a single law of truth. He lived a "righteous way of life" in every respect. He upheld the set boundaries of truth and of sin. He exhibited the charactistics of truth in His life time and never strayed from them.
"Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me." (John 14:6)
Righteous is truth because sinners detest truth, they reject truth. Their lives are lived in sin and set far apart from truth. All who seek the truth reject sin and all who reject sin live in truth.
"And they shall turn away their ears from the truth, and shall be turned unto fables." (2 Tim. 4:4) - "they" is referring to sinners
"Not giving heed to Jewish fables, and commandments of men, that turn from the truth." (Titus 1:14)
"Perverse disputings of men of corrupt minds, and destitute of the truth, supposing that gain is godliness: from such withdraw thyself." (1 Tim. 6:5)
"Therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth." (1 Cor. 5:8)
Truth is what the church is founded on because it is the body of Christ. Christ is the head of the church, the Holy Word directs the church, and the people of the church reject sin. All three ingredients are the very definitions of truth itself so the church must be of the truth and following the truth (that is if it abides by the ideas set forth by Christ and the Bible).
Truth is righteousness, is Godly living, and is the way to true life.
If you accept my words and store up my commands within you, turning your ear to wisdom and applying your heart to understanding, and if you call out for insight and cry aloud for understanding; and if you look for it as for silver and search for it as hidden treasure, then you will understand the fear of the Lord and find the knowledge of God. Proverbs 2:1-5