Ezekiel 1:17

The two wheels are the New and the Old Testament; the Old moves within the New and the New within the Old.

Where else do the divine utterances go, if not to the hearts of men? But going through four parts they were going, because Sacred Scripture goes to the hearts of men through the law, signifying mystery. Through the prophets it goes somewhat more openly, prophesying the Lord. Through the Gospel it goes, presenting the one whom it prophesied. Through the apostles it goes, preaching him whom the Father presented for our redemption. Therefore the wheels have faces and ways, because the sacred utterances show knowledge of precepts together with the performance of works. And they go through four parts, because they speak in distinct times, as we have said, or certainly because they preach the incarnate Lord in all regions of the world. Concerning these it is openly added shortly after: And they did not turn back when they walked. These things were said above concerning the living creatures, but the same things cannot be understood concerning the wheels as concerning the living creatures. Indeed, we said that the wheels signify the Testaments. And the Old Testament did walk, because it came to the minds of men through preaching, but it returned back upon itself, because according to the letter it could not be preserved in its precepts and sacrifices until the end. For it did not remain without change, since spiritual understanding was lacking in it. But when our Redeemer came into the world, He caused to be understood spiritually what He found being held carnally. And so while its letter is understood spiritually, all that carnal observance in it is vivified. But the New Testament was also called the eternal testament through the pages of the Old Testament, because its understanding is never changed. Therefore it is well said that the wheels going went forward and did not turn back when they walked, because while the New Testament is not rescinded, while the Old is now held as spiritually understood, they do not go back upon themselves, since they persist unchangeable until the end of the world. Therefore they walk but do not turn back, because they come spiritually to our heart in such a way that their precepts or pursuits are not changed any further.