Jeremiah’s extension of Jerusalem
Interpretations of Gehenna that appeal to events of 70 AD miss the significance of the prophecies of Jeremiah about the future of the valley of Hinnom, which say that it will become “holy unto the Lord.” This is easily understood, when Jesus’ references to Gehenna are seen in the context of a judgment, which those who are accounted unworthy to enter the kingdom of heaven and the holy city must endure.
While in the prophecies of Isaiah and of Zechariah Jerusalem was to be raised up, in Jeremiah’s prophecy, Jerusalem was to be enlarged, or extended beyond the boundaries of the walls that existed in his time. Isaiah said Jerusalem and Mount Zion would be “established in the top of the mountains” and “exalted above the hills.” [Isaiah 2:1-3] Zechariah said Jerusalem would be “lifted up” and “and inhabited in her place” while the surrounding country would become “as a plain.” [Zechariah 14:9]
A very curious enigma is apparent when we compare the prophecies of Isaiah and Zechariah about Jerusalem being raised up on the one hand, and the prophecy of Ezekiel 47:1-12, about a river flowing from the temple towards the east, on the other. The river in Ezekiel 47 gradually increases in depth. The gradient of the land implied by Ezekiel’s prophecy does not fit the existing topography, in the area between the site of the temple and the mount of Olives, as he described the water first at his ankles, then at his knees, and then at his loins, etc, as he walked towards the east, and it implies that the depth of the river increases at a rate of about three feet in the distance of about half a mile, which is the gradient one might find on a large parking lot, or on a football field. If Jerusalem were raised up, as Isaiah and Zechariah’s prophecies say, the slope of the land would be much greater, and so the problem of how such a gradient of the river would be possible, is increased.
The solution is plain: Ezekiel’s river is not a literal one, and the prophecies of Isaiah and Zechariah about Jerusalem becoming “raised up” refer to the heavenly Jerusalem, not the earthly one. It was “raised up” when Jesus ascended to heaven, Acts 1:9. The river described by Ezekiel represents the gospel going forth from the church. Zechariah gives a similar prophecy in Zechariah 14:8; he says these are rivers of “living water,” and Jesus identified “rivers of living water” with the Spirit. [John 7:38-39]
Consider Jeremiah’s prophecy about the extension of the boundaries of Jerusalem, in Jeremiah 31. This chapter contains a prophecy about a new covenant, [Jeremiah 31:31-34] which is quoted in Hebrews 8:8-12 and 10:16-17, and applied to the church. Jeremiah wrote:
Behold, the days come, saith the LORD, that the city shall be built to the LORD from the tower of Hananeel unto the gate of the corner.
And the measuring line shall yet go forth over against it upon the hill Gareb, and shall compass about to Goath.
And the whole valley of the dead bodies, and of the ashes, and all the fields unto the brook of Kidron, unto the corner of the horse gate toward the east, shall be holy unto the LORD; it shall not be plucked up, nor thrown down any more for ever.
These verses describe the future boundaries of the city, referring to seven landmarks. These landmarks are the Tower of Hananel, the Corner Gate, the hill Gareb, another hill named Goah or Goath, the valley of dead bodies and ashes, the fields as far as the brook Kidron, and the Horse Gate. The order in which these seven places are mentioned is as if the prophet was making a circuit of the city in a counterclockwise direction, beginning at the northeast of the city.
The Tower of Hananel was located in the north wall of the city, near the northeast corner. It was between the fish gate and the sheep gate. [Nehemiah 12:39] In Zechariah 14:10 it represents the northern limit of the city, while the king’s winepress is the southern limit.
The Corner Gate marked the northwest limit of the city. It marked the western limit, in Zechariah 14:10, while in that verse, Benjamin’s gate marks the eastern limit. It was associated with the Ephraim Gate in 2 Kings 14:13 and 2 Chronicles 25:23, so it must be located at the northwest corner of the city.
Gareb means “scabby,” and refers to a hill which was the dwelling place of lepers, outside of the city. Its precise location is uncertain, but it was no doubt a hill to the west of the city.
Goah, or Goath, means “lowing” (Easton’s Bible Dictionary; Smith’s Bible Dictionary) or “his roaring” (Hitchcock’s Bible Names Dictionary). It may possibly be Abu Tor (Giv’at HaNanya; lit. “Father of the Bull”), bounded by the Valley of Hinnom on the north.
The valley of dead bodies is the Hinnom Valley or Gehenna.
The fields as far as the brook Kidron extends the boundaries of the city eastward to the brook Kidron.
The Horse Gate opened upon the Valley of Kidron, and was located in the east wall, near the Temple. 
Jeremiah’s prophecy about the extension of Jerusalem’s boundaries indicates that the valley of Hinnom or Gehenna will eventually be included in Jerusalem, which represents the holy city, the saints. This is significant in the light of statements by Jesus about Gehenna; he referred to it as a judgment, that Christians are encouraged to avoid, at all costs, even if it means suffering the loss of an eye, or a hand, or a foot. The prophecy of Jeremiah shows the intended results of the judgment that Gehenna represents. In Revelation 7, two groups are described. The first group, of those who are sealed, represent the saints, who are also described in Revelation 14:1-5. They are “the firstfruits unto God and to the Lamb.”
John says: “in their mouth was found no guile: for they are without fault before the throne of God.” [Revelation 14:5] They are the ones who gain entry to the holy city, and who are included in the new covenant. The second group, the great multitude which no man can number, includes all those who missed out, and who are “left behind” at the coming of Christ. John said, “These are they which came out of great tribulation, and have washed their robes, and made them white in the blood of the Lamb.” [Revelation 7:14] “They shall hunger no more, neither thirst any more; neither shall the sun light on them, nor any heat. For the Lamb which is in the midst of the throne shall feed them, and shall lead them unto living fountains of waters: and God shall wipe away all tears from their eyes.” [Revelation 7:16-17]
1. For a scholarly study on each of these locations, and a review of several interpretations of Jeremiah’s prophecy, see: Dennis M. Swanson. Expansion of Jerusalem in Jer 31:38-40: never, already or not yet? The Master’s Seminary Journal 17/1 (Spring 2006) 17-34.