What does Genesis 26:30 mean?

Isaac's prior relationship with the king of Gerar was strained. He was caught in a dangerous lie regarding his wife, Rebekah (Genesis 26:6–11). When Isaac's prosperity threatened the king, the king asked him to move away (Genesis 26:14–16). Even then, the people of the region harassed Isaac's family about the use of wells (Genesis 26:18–22). After Isaac moved to Beersheba, the king and his entourage arrived to have a conversation (Genesis 26:26).

In the previous two verses, King Abimelech explained to a suspicious Isaac (Genesis 26:27) that he had come to make a peace treaty with him because he and his advisors could clearly see that Isaac was blessed by God (Genesis 26:28–29).

Isaac apparently approves. Instead of turning them away, he decides to show them hospitality in the form of a feast with eating and drinking. This reflects the common sense of how to treat guests, of that time, as well as Isaac's presumably good intentions. It's noteworthy, also, that Isaac is hosting a feast for a king—another reflection of his enormous prosperity.