John Chrysostom
He says this about the New Covenant, after saying, "not like the covenant which I made." What other difference between them is there, if not this?
If someone says that this phrase does not express the distinction of the New Covenant, but only that it was given into their hearts, and that here the difference is not in the commandments but in the manner of their communication, let him prove it.
The covenant, he says, will no longer be in writing, but on hearts. Let such a person prove that this ever happened among the Jews.
It cannot be proved. Even after their return from Babylon, the covenant was again given to them in writing. But the Apostles, as I can prove, received nothing in writing, but received everything in their hearts by the Holy Spirit.
Therefore Christ said to them, "When the Comforter comes, whom I shall send to you from the Father, the Spirit of truth who proceeds from the Father, He will bear witness to Me" (Jn 15:26).