Updated: Apr 4, 2021
The below write-up on "truth" is an excerpt from the Catholic Bible Dictionary with General Editor, Scott Hahn. This is one of the best understanding of "truth" as given in the Bible, that I have come across.
Truth is reality as correctly perceived by man or made known by God through revelation. In the Bible, truth is often connected with the tenets of Israelite or Christian faith. Religious truth includes the ideas of "facticity" as well as "fidelity." In other words, in biblical terminology (Hebrew 'emet; Greek aletheia), truth tells us the way things really are, whether in reference to God, man or the created order in general, and it does so in a way that is completely reliable and trustworthy. Knowledge of the truth has the power to set us free from the cynicism and skepticism and nagging uncertainties that plague the world (John 8:31-32).
I. In the Old Testament
"Truth" in the Old Testament suggests constancy, faithfulness, and something worthy of our confidence and hope (Genesis 24:27, Genesis 47:29; Joshua 2:14; 2 Samuel 2:6, 2 Samuel15:20; 2 Kings 20:19; Hosea 2:20). The OT proclaims that God is the source of all truth and guarantees His words, promises, and faithfulness, which "endures to all generations" (Psalm 119:90; cf. Psalm 31:5, Psalm 119:142; Jeremiah 10:10). God's word is true; in fact, it is the standard of truth (2 Samuel 7:28; Psalm 119:89). Truth is His wisdom and commands and governs all of creation (Proverbs 8:7).
Since God is truth, those who live in fidelity to Him are called upon to live in truth and to bear witness to the truth. Thus the eights commandment forbids bearing false witness (Exodus 20:16; Deuteronomy 5:20). There is truth to be apprehended in the investigation of facts or events (Deuteronomy 17:4; 1 Kings 10:6). Truthfulness is also an attribute of a person: "Let one of you go and bring your brother, while the rest of you remain in prison, in order that your words may be tested, whether there is truth in you" (Genesis 42:16).
II. In the New Testament
Truth has the same meanings in the New Testament as in the Old Testament, but under the influence of Greek philosophy it can be more intellectual; it is a reality to be apprehended by the mind. The concrete understanding of truth as stability and dependability is still present (2 Corinthians 7:14), especially as it pertains to God (Romans 3:7, Romans 15:8, 1 Peter 5:12). But the abstract sense of "truth," the correct perception of reality, is also very important to New Testament writers (Mark 5:33; John 5:34, John 16:7, John 6:13, John 19:35; Acts 26:25; Romans 9:1; 2 Corinthians 12:6; Ephesians 4:25).
The New Testament proclaims that in Jesus Christ the whole of God's truth has been revealed, for Jesus us the truth (John 1:14, John 8:12): "I am the way, the truth, and the life" (John 14:6). By following Jesus, the disciple is led by the Spirit of truth and "He will guide you into all the truth; for He will not speak on His own authority, but whatever He hears He will speak and He will declare to you the things that are to come" (John 16:13).
The Christian faith is the truth (Galatians 2:5; Ephesians 1:13), and believers are challenged to live in conformity with it - for "If we say we have fellowship with Him while we walk in darkness, we lie and do not live according to the truth" (1 John 1:6). To find this truth, one need only believe in the Gospel (1 Timothy 2:4), "and you will know the truth, and the truth will make you free" (John 8:32; cf. John 17:17). That freedom is possible by the power of Christ, and it brings with it the inner transformation of the person by freedom's encounter with the truth (James 1:18; 1 Peter 1:22; 2 Peter 1:12).