God had delivered His people from Egypt, and had united them to Himself in order that they might be separated from all the nations. And having brought them out of Egypt, and joined them to Himself, He said of them, "The people shall dwell alone and shall not be reckoned among the nations" (Num. 23:9). It was only by remaining faithful to their union with God that they could be separated from all the nations. (Ex. 33:16).
Israel was then the church, -- "the church in the wilderness" (Acts 7:38). That church was united to God in solemn covenant, upon which the Lord said, "I am married unto you," and, "I was an husband unto them." Thus was that church united to God. And in this there was the complete separation of Church and State.
But Israel was unfaithful to God. She rejected Him and set up a State, and thus formed a union of Church and State. The result was the complete ruin of the State which they had formed; the scattering of the people in captivity among the nations; and the desolation of their land. In their captivity and their trouble they sought the Lord in contrition; and joined themselves again in faithfulness to Him. And this brought them back to their original position of being the church only, and so to their original condition of total separation of Church and State.
God had planted Israel -- His church -- in Canaan to be the light of the world, to give the knowledge of the true God; as at that time and for ages afterward Palestine was the pivot of the known world. By their being faithful to Him and having Him abide with them, He intended that they should influence all the nations for good. But they revolted and became not only "like all the nations," but even "worse than the heathen." Therefore the land became sick of them, and spewed them out, as it had spewed out the heathen before them. (Lev. 18:25, 28; 20:22).
As by their apostasy and union of Church and State, Israel had frustrated God's purpose to enlighten all nations by them in the land where He had planted them, He would fulfill His purpose, nevertheless; and, separating them again entirely from the State, would enlighten all the nations by them in the lands where He had scattered them. Israel, by becoming like all the nations, had lost the power to arrest and command the attention of all the nations, that the nations might know God, and be taught of Him. Nevertheless, God would now use them to enlighten those who, under Him, had acquired the power to arrest and command the attention of all the nations. Thus by them still He would bring to all the nations the knowledge of the true God, and teach them that "the Most High ruleth in the kingdom of men, and giveth it to whomsoever He will" (Dan. 4:17). This is the whole philosophy of the captivity and subjection of Israel and Judah to Assyria, Babylon, Medo-Persia, Grecia, and Rome.