It's a slightly skewed reference to Isaiah 11:
The wolf also shall dwell with the lamb, and the leopard shall lie down with the kid; and the calf and the young lion and the fatling together; and a little child shall lead them. And the cow and the bear shall feed; their young ones shall lie down together: and the lion shall eat straw like the ox. And the sucking child shall play on the hole of the asp, and the weaned child shall put his hand on the cockatrice' den. They shall not hurt nor destroy in all my holy mountain; for the earth shall be full of the knowledge of the Lord, as the waters cover the sea.
It's a reference to the Messianic Age, and is followed by a reference to the second great regathering of the Jewish people to the Land of Israel.
Before lions and calves (it's not lions and lambs: it's wolves and lambs, and lions and calves) lying down together has prophetic significance, we need to see a second great regathering. We have seen the beginning of the first one, begun in 1948; but it's not finished yet (there are still more Jews in the US than there are in Israel), and there must be another Diaspora (probably the Time of Jacob's Trouble, or Tribulation, prophesied in Zechariah and in Revelation) before the second great regathering can begin.
Both the second great regathering and the reversion of carnivores to herbivorism are things that will happen when Messiah returns, according to Isaiah. (He speaks of this also at the end of chapter 65.)
In other words, this is not a sign of the apocalypse.
But it is fascinating.