Why God can’t lie (or sin)
The idea of an All-Perfect Being lying involves a logical contradiction, just like the idea of a square circle.
Scripture repeatedly affirms the truthfulness of God. As early as the book of Numbers, we read:
God is not man, that he should lie, or 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 fulfil it? (Num. 23:19).
The same view is expressed in multiple other passages (e.g., 1 Sam. 15:29, 2 Tim. 2:13, Tit. 1:2). Jesus even declares himself to be “the Way, the Truth, and the Life” (John 14:6).