Lamentations 2:16
All thine enemies have opened their mouth against thee: they hiss and gnash the teeth: they say, We have swallowed her up: certainly this is the day that we looked for; we have found, we have seen it. All thine enemies have opened their mouth against thee: they hiss and gnash the teeth: they say, We have swallowed her up: certainly this is the day that we looked for; we have found, we have seen it.
Jeremiah wrote it as part of a sad song commemorating the awful sufferings that came upon the apostate people of God, the inhabitants of Jerusalem, closing the lessons begun in Jeremiah 40. It portrays Jerusalem's enemies opening their mouths against her, hissing and gnashing their teeth, claiming to have swallowed her up. They celebrate that the long-awaited day they hoped for has arrived and been seen, expressing satisfaction at seeing God's people become a reproach and a prey to them.
It marks the fulfillment of the Lord's warnings after the people rejected his counsel, when Jerusalem fell and its people went into Babylonian captivity. It describes the severe tribulation Jerusalem suffered under its enemies, with further detail about that suffering given in Lamentations 4:3-10. The Jews' tribulation under the Babylonians was at least as great as the tribulation associated with Jerusalem's later destruction. The destruction brought tribulation comparable to the suffering under the Babylonians, so Jerusalem's later destruction was not the uniquely greatest tribulation described in Matthew 24.
The verse illustrates how one's point of view shapes how a moment is seen, and it can be applied to a long-awaited turning point such as the end of one century and the beginning of another, even though the circumstances differ from Jeremiah's day. The verse warns that lukewarmness and sin can leave God's people exposed to their enemies' scorn in distress.