"Moreover, the Faithful One of Israel does not deceive or repent" I Samuel 15:29
The haftarah tells the story of Saul's downfall, wrapped up in the package of the war against Amalek. The chapter begins by God telling Samuel to instruct Saul to take revenge against the Amalekites for what they did to the children of Israel after they fled Egypt.
The instructions are explicit: kill everyone, destroy everything, spare no one and nothing (not even the livestock). But somehow Saul can't manage to get this simple instruction right. His army are not keen to destroy valuable animals and Saul, himself, leaves Agag, the king of the Amalekites, well and truly alive. Already by verse 11, God expresses regret: nichamti, "I regret that I made Saul king". Samuel duly chastises Saul for his failure to follow orders and Saul is, in return, repentant.
So we might have expected God to be forgiving - that is, after all, what we might reasonably presume of a merciful deity. But in verse 29 we are told explicitly that God does not yenacheim, God does not change His mind; "for God is not human that He should l'hinacheim, repent." In other words, God will not be swayed by Saul's contrition. For Saul there is no forgiveness, no redemption.
What is especially peculiar here is that in verse 11 God repents and then in verse 29 the text states that God does not repent, ever; repentance is a human foible. How are we to reconcile this theological conundrum? How can God so baldly contradict God's self in the space of a handful of verses? The commentators are strangely silent.
The Targum is so vexed that its "translation" strays some great distance from the literal meaning of the verse. There is no simple answer, only the realisation that God is neither entirely merciful nor consistent.