Part of the ongoing Verse Quick Reference project.
Num 23:19 God is not man, that he should lie, or a son of man, that he should change his mind. Has he said, and will he not do it? Or has he spoken, and will he not fulfill it?
Numbers 23:19 is often quoted as a prooftext for immutability. This quote is said to show that God cannot change in any way, shape, or form. But, contextually, there is likely a better understanding of this verse.
In context, God has intercepted a false prophet, Balaam, from declaring that Yahweh was against Israel. God threatens Balaam into proclaiming blessing, not curses for Israel. Balaam complies, and informs the enemies of Israel that “God is not a man that He should lie or a son of man that He should change His mind.” Contextually, the point is that God has declared blessings for Israel and will not just change His mind. God has spoken, and God will fulfill.
The context is God’s promises towards Israel. God is not fickle in His promises. The context says nothing about God’s essence, being eternally immutable in every respect, or even being impassible. Contextually, at best, this is a prooftext for God never changing His mind. More likely, however, this is a generality (as is common in human communication) and means simply that God is not arbitrary. God does change His blessings into curses throughout the Bible, but it is for reasons such as Israel rebelling against God. No such third party factors are at play in the Numbers verse.
A false prophet is speaking these words, granted under duress from God. Even if the speaker was arguing for pure immutability, the words need to be taken with a grain of salt. Surely, the reoccurring words from God about Himself describing God’s own change of mind have more weight than a false prophet. This text is a poor prooftext for immutability.