Augustine of Hippo, on Heb 8:8

Prophetic utterances are of three kinds: (1) some relating to the earthly Jerusalem; (2) some to the heavenly Jerusalem; (3) and some to both simultaneously. I think it proper to prove what I say by examples. The prophet Nathan was sent to convict King David of heinous sin and predict what future evils would happen to him because of his sin. Who can question that this pertains to the earthly city? There are other instances, sometimes addressed to the public at large for their safety and benefit, and sometimes addressed to someone in private who merited an utterance from God in order to know in advance about some event to guide his temporal life.The following prophecy, however, without a doubt references the heavenly Jerusalem. "Behold, the days are coming, says the Lord, that I will make for the house of Israel, and for the house of Judah, a new testament: not according to the testament that I settled for their fathers in the day when I laid hold of their hand to lead them out of the land of Egypt; because they continued not in my testament, and I regarded them not, says the Lord. For this is the testament that I will make for the house of Israel: after those days, says the Lord, I will give my laws in their mind, and will write them upon their hearts, and I will see to them; and I will be to them a God, and they shall be to me a people." Here, God himself is Jerusalem's reward. Its chief and entire good is to possess him and to be possessed by him.
Both cities are indicated when the city of God is called Jerusalem and when it is prophesied that the house of God shall one day be in Jerusalem. This prophecy seems to be fulfilled when King Solomon builds that most noble temple. For these things both happened in the earthly Jerusalem, as history shows, and were types of the heavenly Jerusalem. This kind of prophecy, as it were, blending both the others in the ancient canonical books devoted to historical narratives, is very common. It has exercised and continues to exercise greatly the talents of those who search holy Scripture.