Therefore, behold, the days come, saith the LORD, that this place shall no more be called Tophet, nor The valley of the son of Hinnom, but The valley of slaughter.
This place shall no more he called Tophet - from the Hebrew top (H8596), a drum; because in sacrificing children to Moloch drums were beaten to drown their cries. Thus the name indicated the joy of the people at the fancied propitiation of the god by this sacrifice; in antithesis to its joyless name subsequently.
Valley of slaughter - it should be the scene of slaughter, no longer of children, but of men; not of "innocents" (Jeremiah 19:4), but of those who richly deserved their fate. The city could not be assailed without first occupying the valley of Hinnom, in which was the only fountain; hence arose the violent battle there.