What is the Biblical basis that God “cannot” act against his nature?

We are fallible; we call that “original sin” and if you want to understand this, compare what Mother Theresa would do in any situation you can think up, then hold yourself to that standard.

You lose. QED

GOD is beyond our ability to understand. Ask this dumb question: “Can GOD make a stone too big to roll?” Clearly, YES. “And then can GOD roll it?” Clearly, YES.

GOD is beyond any definition or understanding our little three pound we computer can dream up.

Next question.