"Why do you say it is impossible for God to lie? God has all power and can do anything if he wants to!" This reader certainly has not read his Bible! Paul answered this very question twice in the New Testament. To Titus he wrote that God "cannot lie" (Titus 1:2) and in Hebrews 6:18 he declared it is "impossible for God to lie."
But why should it be impossible for God to lie — if God can do all things? The answer ought to be obvious.
First, consider this — God is perfect character. Character is a matter of the will. God has willed, determined, chosen always to tell the truth. God cannot lie because He will not lie. No trait of character is more important than this. If God could not be relied upon, then His Word, the Bible, would have no authority.
It takes a strong character always to tell the truth. Anyone who lies is a weak character. It is easy to lie. It is human to lie. Truth, by contrast, is an attribute of God — a trait of divine character.
When one is born of God and possesses the fullness of divine character, it will be impossible to sin — impossible to lie (I John 3:9).