Isa 21:8   And he cried, "A lion: My LORD, I stand continually upon the watchtower in the daytime, and I am set in my ward whole nights:

     This phrase "A lion" is the Hebrew word "ro'eh", meaning 'a seer (as often rendered); but also (abstractly) a vision' (Strong's no. 7203). The idea is that he saw an army approaching, strong 'as a lion'.¹
     This 'watchman' is calling out to The LORD (Hebrew 'Adonay') Who appointed him, and he is revealing that the destruction of Babylon is imminent, soon to happen. But what he first saw evidently had moved on to somewhere else, as he declares, "I am set in my ward whole nights:”

Isa 21:9   And, behold, here cometh a chariot of men, with a couple of horsemen." And he answered and said, "Babylon is fallen, is fallen; and all the graven images of her gods he hath broken unto the ground."

     This event happened to ancient Babylon when the Persians ("he" meaning 'Cyrus' probably) and Medes caused its destruction. The phrase "a couple of horsemen" means a military troop by rows of two's. But this is only a type for the destruction of a final false Babylon being setup in today's time. Consider the following from Revelation:

Rev 18:1   And after these things I saw another angel come down from heaven, having great power; and the earth was lightened with his glory.
2    And he cried mightily with a strong voice, saying, "Babylon the great is fallen, is fallen, and is become the habitation of devils, and the hold of every foul spirit, and a cage of every unclean and hateful bird.

     These verses from Revelation 18 have not happened yet today. Notice that the phrase "Babylon the great is fallen, is fallen" is almost the same words as given here in Isaiah 21:9? One can't apply this to a Preterist view, that Revelation is all past, as this example for our future is being declared by an "angel", not a flesh man as Isaiah here in Isa.21. These verses speak about the future final destruction of the Babylon 'system' which has plagued mankind throughout flesh age history. The Revelation examples prove that the old system of ancient of Babylon is a blueprint for the future final Babylon, which is nearly upon us.

Isa 21:10   O my threshing, and the corn of my floor: that which I have heard of the LORD of hosts, the God of Israel, have I declared unto you."

     This is Isaiah the prophet speaking. The meaning of the word "threshing" here is toward Isaiah's down-trodden people ('medushshah' - Strong's no. 4098). And the phrase "and the corn of" is actually the sole Hebrew word "ben", meaning 'sons' (Strong's no. 1121). And the word "floor" does literally means a 'threshing floor', where the impurities of grain are separated. So what does all this mean? Remember earlier how I covered the analogy of being 'with child' spiritually? Isaiah is grieving for his own people who allowed themselves to be deceived by the system of Babylon.
     This 'threshing' floor analogy should be understood in the sense of our Father's Righteous Judgments. Well, if you've stayed in Him, and wait upon His True Son Messiah Jesus Christ, not falling away to false worship during our future, then what sort of judgment can you expect from our Father? Obviously then, a 'judgment' can be good also, in the sense of reward for waiting upon The Lord. And just as our Father is very accurate in punishment, likewise He is very accurate in giving rewards to His People who stay in Him through His Son:

Amos 9:8   Behold, the eyes of the Lord GOD are upon the sinful kingdom, and I will destroy it from off the face of the earth; saving that I will not utterly destroy the house of Jacob, saith the LORD.
9    For, lo, I will command, and I will sift the house of Israel among all nations, like as corn is sifted in a sieve, yet shall not the least grain fall upon the earth.
10    All the sinners of My people shall die by the sword, which say, "The evil shall not overtake nor prevent us."