What does Genesis 26:10 mean?
In the prior verses, Isaac repeated one of his father's failures by lying about his wife, to protect his own life (Genesis 20:2–6). Abimelech's accusation in this verse is absolutely right. Isaac failed to face the possibility of protecting himself, or his wife, from someone who might try to take her from him. This cowardice has put Abimelech's whole kingdom at risk of violating a marriage—something even a pagan nation of that era apparently considered a grievous mistake.While it's all but certain this is not the exact same Abimelech who dealt with Abraham—in a very similar situation in Genesis 20—this king most likely knows that story. At that time, the Lord came to Abimelech in a dream and called him a dead man for innocently taking Sarah to be his wife because of Abraham's lie. This Abimelech is aware of the great guilt that would have fallen on him and/or his people if one of them had done the same with Rebekah. His anger is justified.
Again, Isaac's failure to trust God has led to grave danger for those near him. He, however, continues to be protected by God's promise to be with him, as the following verse will make clear.