Johannes Quasten, Patrology, vol. III: The Golden Age of Patristic Literature (Westminster: Christian Classics, 1990) 331.
Eusebius was a Christian thinker in the third-fourth centuries C.E. He wrote Demonstratio Evangelica in response to Jewish critics of Christianity. Quasten states:
The first two books, which form the introduction, explain why the Christians accept the Jewish Scriptures but reject the legislation of Moses. Christianity is a continuation of the world-wide religion of the patriarchs, from which the Mosaic law was only a temporary dispensation, serving as a transition between the age of the patriarchs and the coming of Christ.
As I read this, I wondered why Eusebius believed that God gave the Torah. I found Book 1 to contain interesting details about Eusebius' view on the law.
For Eusebius, Christian piety is a return to the type of religion that pre-existed the Mosaic law. Eusebius points out that, prior to the law of Moses, Abraham was justified by faith, and God's people could worship anywhere they pleased. Eusebius also compares the principles of the Sermon on the Mount (Matthew 5-7) with Job's lifestyle, for Job refused to lust after women and rejoice at the fall of his enemies.
One area in which pre-Mosaic and Christian piety differ, however, was on animal sacrifices, for Abel, Job, Abraham, etc. offered them, whereas Christian sacrifices are more spiritual (e.g., good works, prayer, praise, etc.). For Eusebius, the animal sacrifices served to ransom the worshipper, as the animal's life substituted for his own (yes, the doctrine of substitutionary atonement predated Anselm). But Christians now have Christ for their ransom from sin, so they don't need to offer animals.
Eusebius doesn't think that the pre-Mosaic saints needed the Mosaic law, since they were doing a fairly decent job being good without it. But the Israelites went to Egypt, and there they became corrupted by Egyptian idolatry and immorality. As a result, God gave them the law of Moses to place and keep them on the right track. And God was pretty strict too. Eusebius says more than once that God was treating Israelites as if they were helpless children, who'd rush to do evil without proper restrictions and discipline. That's why God only allowed them to sacrifice in one place, the central sanctuary.
But Eusebius does not believe that the Mosaic law was ever intended to be universal or permanent, for it was obviously designed for the children of Israel while they were living in the Promised Land (or at least near the tabernacle). It required them to worship, sacrifice, and become cleansed in the place where God chose, the central sanctuary, and that could not be done outside of the land of Israel. That means that Gentiles and Diaspora Jews could not observe the law of Moses.
For Eusebius, God made the Torah this way because he knew that the Jews' central sanctuary would one day be destroyed--in 70 C.E. At that time, God would offer them a new law, one that said God could be served and worshipped in any place, not just the central sanctuary. The Old Testament prophets predicted this scenario when they discussed legitimate altars and worship outside of the land of Israel (i.e., Isaiah 19:19's reference to an altar in Egypt; Malachi 1:11's statement about the nations offering incense to the LORD). But, to Eusebius' sorrow, the Jews have rejected God's new law, the Gospel of Jesus Christ, falsely believing that they're observing the law of Moses, even though they can't keep its commands regarding the central sanctuary.
There are two questions I have about Eusebius' scenario:
1. Does Eusebius believe that the Israelites needed to be purified from Egyptian influence for over a thousand years, which is the time between their departure from Egypt and the first coming of Christ? Maybe he thinks that this was the initial reason for the Mosaic law, but afterwards there were other temptations for Israel to succumb to idolatry and immorality (i.e., the Canaanites). God tried to keep them on track with his Torah, but they still succumbed to evil, which is why God chastised them for disobeying his strict law.
2. Why does Eusebius believe that God gave Israel the Torah? Okay, I understand that God led them to Egypt, where they became corrupted, and God then gave them the Torah to place them on some path of righteousness (though it fell short of the pre-Mosaic and New Covenant standards). But why did God go that route? Why didn't he stick with the pre-Mosaic system of doing good and worshipping God wherever one pleases?
I couldn't find Eusebius' answer to this question, but perhaps he thought that God wanted some oasis of truth amidst a world of godlessness and immorality, and that's why he established the nation of Israel as a light to the nations. An entire nation could publicize God, righteousness, and the drama of God's activity in history better than righteous individuals. God promised to establish such a nation through Abraham, but she lost her way in Egypt, so God gave her the Torah to keep her on track. But the Torah was setting the stage for something greater, the New Covenant.
At least that's one way of seeing it. I'm sure Jewish interpreters conceptualize the issues differently!