This reference to Isaac is the only place in the Old Testament where Isaac stands for the nation of his descendants rather than for the person himself. Perhaps Amos has in mind the special veneration for Isaac shown by the northern kingdom as they make pilgrimages to Beersheba (Amos 5:5; Amos 8:14), Isaac’s birthplace (Genesis 21:31).1
High places were shrines built on hills in the open country. They were based on the idea that the higher up you go, the closer you get to God.2
9 the high places of Isaac shall be made desolate, and the sanctuaries of Israel shall be laid waste, and I will rise against the house of Jeroboam with the sword.”