Augustine wrote: “The New Testament is in the Old Testament concealed, the Old Testament is in the New Testament revealed.”
When Paul was writing his epistles he didn’t have much New Testament writings to draw from that we know of. He was aware of some of the other apostles writings (as they were of his) but he is clear that the main part of what he wrote was revealed to him directly (see for example Ephesians 3:2-11). In his writings Paul makes allusions to Old Testament types and shadows (e.g. Gal. 4:21-31), reveals the meanings behind many Old Testament prophecies and writings (e.g. Eph. 4:8-13) and draws on the experiences of the people of Israel to warn and admonish the New Testament churches to which he wrote (e.g. 1 Cor. 10:1-11).
Hezekiah’s Tunnel is a physical, Old Testament, engineering work. Like other physical things spoken about in the Old Testament, it is a shadow or reflection of a spiritual reality. Physically and spiritually it exists in the the City of David which is situated on Mount Zion and is part of Jerusalem in the land of Judah and Israel. David is considered the archetype or forerunner of Jesus – he and his rule over Judah and Israel, his reign in Jerusalem, was the OT physical representation of the spiritual truth of Jesus’ current reign in His NT church.
Probably the best place to see how this works out in practice is found in the Psalms. Psalm 87 is particularly instructive. Once you get the pictures and symbols in this Psalm you can apply them all over the OT:
A Psalm of the sons of Korah. A Song.
His foundation is in the holy mountains.
2 The Lord loves the gates of Zion
More than all the dwellings of Jacob.
3 Glorious things are spoken of you,
O city of God! Selah
4 “I will make mention of Rahab and Babylon to those who know Me;
Behold, O Philistia and Tyre, with Ethiopia:
‘This one was born there.’ ”
5 And of Zion it will be said,
“This one and that one were born in her;
And the Most High Himself shall establish her.”
6 The Lord will record,
When He registers the peoples:
“This one was born there.” Selah
7 Both the singers and the players on instruments say,
“All my springs are in you.”
In this Psalm Jerusalem is called the city of God. The spiritual counterpart is the Church or Body of Christ worldwide. Each local church should also be a mini city of God with the same elements as are described here.
The foundations of what God does (v.1) in the earth are in these holy mountains of which Zion (vv. 2& 5) is the central one, the dwelling place of God’s shekinah glory and the place from which every born again believer is birthed spiritually. It is up to us to ensure that God dwells in the manifestations of Zion that are our local churches. To do this requires maintaining walls and digging tunnels to bring the life giving waters – which are outside the walls – into the healing centre of the church.
Let the Lord teach you these things. They will inform your reading of the OT and bring it alive in a way you may not have experienced before. Read the Old Testament with New Testament eyes.
[Please note that I am not a replacement theologian, there is something very significant happening with the physical current day people of Israel and the believers in their midst. That is just not the subject of this particular teaching.]