Why did Israel assume they had nothing to worry about as children of the covenant?
Israel assumed that being children of the covenant, the prophets, and the promises guaranteed their standing, so they thought they had nothing to worry about and were secure. They trusted physical descent from Abraham rather than faith, but covenant promises ran only through Isaac and Jacob, not every biological descendant.
Les explains in Romans 9 that not all who are genetically from Abraham are children of promise. Ishmael and Esau had offspring, but spiritually they were outside the covenant promises. The promises could only go to the offspring of Isaac and Jacob down that family tree. Israel became puffed up and arrogant, saying that because they were children of the covenant, the prophets, and the promises, they had nothing to worry about and were made. Les says Paul will come and blow them out of the saddle, insisting they cannot enter God's promises simply because they are in the right genealogy; they must still enter in by faith.
Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called.
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