God tells the truth and cannot lie. Several passages teach this attribute of God:
(Heb. 6:18) So that by two unchangeable things in which it is impossible for God to lie, we who have taken refuge would have strong encouragement to take hold of the hope set before us.
(Num. 23:19) God is not a man, that He should lie, Nor a son of man, that He should repent; Has He said, and will He not do it? Or has He spoken, and will He not make it good?
(1 Sam. 15:29) Also the Glory of Israel will not lie or change His mind; for He is not a man that He should change His mind.
(Titus 1:2) In the hope of eternal life, which God, who cannot lie, promised long ages ago.
(2 Tim 2:13) If we are faithless, He remains faithful, for He cannot deny Himself.
(Jn. 17:17) Sanctify them in the truth; Your word is truth.
The veracity of God produces a number of practical effects in the life of the believer:
The Bible is inspired and true. If God cannot lie, and the Bible is the Word of God, then how can the Word of God lie?
We can bank on God’s promises. They are a “done deal.” This explains the “already-not-yet” tension in the Scriptures. God can speak of future promises and events in the past tense. That is, these future historical events (e.g. Christ’s return, our reward, our seat in heaven, etc.) are so certain that they are spoken of as though they were already accomplished in the past.