Therefore thus says the Lord GOD,
Behold, I lay in Zion for a foundation a stone, a tested stone, a precious cornerstone, a sure foundation: he that believes shall not be in haste.
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Eusebius of Caesarea
Who can the cornerstone be other than the one who is the living and precious stone supporting two structures with his teaching making them one? He established the building of Moses, which was to remain until his day, and then he joined on to one side our building of the gospel. This is why he is called the cornerstone.