God Is Not A Man

God is not a man, that he should lie, neither a son of man, that he should repent.
--Numbers 23:19a, ASV

And also the Strength of Israel will not lie nor repent for he is not a man that she should repent.
--1 Sam 15:29, ASV

These two verses are interesting in that they virtually reproduce the other. Unlike Samuel, Numbers clearly follows the structure of a poetic parallelism:

A1 - God is not a man
B1 - that he should lie
A2 - neither a son of man
B2 - that he should repent

Theologically, we could say that God cannot lie because to do so would be to go against his own character. But this would ignore a greater depth of meaning. Textually, the Samuel passage also parallels Numbers in terms of narrative. Like the prophet Balaam speaking to king Balak, the prophet Samuel speaks to king Saul. Both sayings are unpleasant to the hearers. Both are in context of Yahweh's promise to establish Israel in the Promised Land. In the first, Balak was trying to stand in the way of this promise by having Israel cursed. In the second, Saul was standing in the way by disobeying the commands of God.

A better understanding of the shared verse then is that unlike men who fail to fulfill the words they place in contract (change their mind) or who fraudulently agree to something without any interest in keeping that agreement from the beginning (lie), Yahweh is faithful to his covenantal promises. The fact that Saul is removed and David set up in his place or that Balaam's curse is turned to blessing are evidences in time and history that validate Yahweh's claim about himself and serve as reminders that just as Yahweh was faithful to his covenant then, so we can be confident he will show himself faithful again.