Why does God deal with Israel throughout the Old Testament?
God deals with Israel throughout the Old Testament to bring the Abrahamic covenant to fruition. He is forming a nation of people, giving them a promised land, and ultimately a government, so Israel becomes unique and separated from all other nations, exactly as the covenant promises.
Les explains that the Abrahamic covenant is a progressive revelation. Within it are the promise of a nation of people, a geographical area of land, and, implicitly, a government. As you move through the Old Testament, all of God's dealing with Israel is to bring this covenant into fruition. Israel will be a unique, separated nation, different from all other nations, placed in the land God promised. Les also notes exceptions like Jonah being sent to Nineveh and Naaman the Syrian, showing that a sovereign God can make exceptions while still primarily dealing with the Jew.
And I will make of thee a great nation, and I will bless thee, and make thy name great; and thou shalt be a blessing: