And he cried, A {l} lion: My lord, I stand continually upon the watchtower in the daytime, and I am set in my post whole nights:

(l) Meaning, Darius who overcame Babylon.

Wesley's Notes

21:8 A lion - The watchmen cried out, I see also a lion marching before the horsemen and chariots: which they suppose to represent Cyrus or Darius marching in the head of their armies. My lord - The watchman speaks to the prophet, who had set him in this station. Whole nights - According to thy command I have stood, and do yet stand continually, both day and night, upon my watch - tower.

King James Translators' Notes

he...: or, cried as a lion

whole...: or, every night

Jamieson-Fausset-Brown Bible Commentary

8. A lion-rather, "(The watchman) cried, I am as a lion"; so as is understood (Isa 62:5; Ps 11:1). The point of comparison to "a lion" is in Re 10:3, the loudness of the cry. But here it is rather his vigilance. The lion's eyelids are short, so that, even when asleep, he seems to be on the watch, awake; hence he was painted on doors of temples as the symbol of watchfulness, guarding the place (Hor. Apollo) [Horsley].

Matthew Henry's Concise Commentary

21:1-10 Babylon was a flat country, abundantly watered. The destruction of Babylon, so often prophesied of by Isaiah, was typical of the destruction of the great foe of the New Testament church, foretold in the Revelation. To the poor oppressed captives it would be welcome news; to the proud oppressors it would be grievous. Let this check vain mirth and sensual pleasures, that we know not in what heaviness the mirth may end. Here is the alarm given to Babylon, when forced by Cyrus. An ass and a camel seem to be the symbols of the Medes and Persians. Babylon's idols shall be so far from protecting her, that they shall be broken down. True believers are the corn of God's floor; hypocrites are but as chaff and straw, with which the wheat is now mixed, but from which it shall be separated. The corn of God's floor must expect to be threshed by afflictions and persecutions. God's Israel of old was afflicted. Even then God owns it is his still. In all events concerning the church, past, present, and to come, we must look to God, who has power to do any thing for his church, and grace to do every thing that is for her good.