And I saw an ANGEL standing in the sun;
What an unusual place for an ANGEL to stand. Or is it? You may recall that the fourth ANGEL with a bowl poured it upon the sun (Revelation 16:8). Even the image below showing us the current sun makes it easy to see how a special sunspot could appear to us on earth as an ANGEL. The sun is constantly being monitored by satellites and radio telescopes, so this appearance of an ANGEL standing in the sun would be relayed throughout the earth.
During the tribulation while the fourth trumpet judgment (Revelation 8:12) was taking place, the sun was darkened. Perhaps the darkened sun erupts with one massive solar flare that looks like an ANGEL.
Most importantly, this ANGEL's appearance shouts to the reader that what is happening next is VERY IMPORTANT.
and he cried out with a LOUD VOICE,
Now this complicates things. There is no inter solar medium such as air to carry the LOUD VOICE of this ANGEL. Hence, we come to one of those unexplainable events, at least in common earth terms, that will captivate the earth. Not only that, the devil and his surrogate armies (verse 19) are given notice as to what their fate will soon be.
When a LOUD VOICE is used (Revelation 6:10; Revelation 7:2; Revelation 7:10; Revelation 10:3; Revelation 14:15; and Revelation 18:2), something IMPORTANT follows. So too, here, watch for the IMPORTANT EVENT.
saying to all the BIRDS which fly in mid heaven,
Earlier in this chapter in verse 9, we witnessed a marriage supper. Now, the BIRDS are invited to God's SUPPER. Again, as in hearing the LOUD VOICE, the BIRDS at least on earth need air in which to fly. And that, in fact, is what surrounds the earth and separates the water below from the water above. God made it that way on the second day of creation (Genesis 1:6-8).
Some expositors tie this verse to Ezekiel 39:17-24 for the language is very similar. There are enough dissimilarities to also say these are not the same. However, one thing is clear from Ezekiel, it is iniquity which is the problem (or bird feed). In Ezekiel, it was iniquity within Israel, in particular, that was the problem; here in Revelation, it is the iniquity or evil of the whole earth. Look at how Jesus referred to this in Matthew 24:15-28.
This may well describe in physical terms a spiritual cleansing or removal of evil from the earth. Evil resides within living beings or in "water". Evil is real, and must be "eaten" by these BIRDS, to remove it from mankind. Much, if not all, evil is based in demons, and demons must go somewhere when they are excised (Mark 5:1-20). The BIRDS will take care of that.
"Come, ASSEMBLE for the GREAT SUPPER of God;
It is God's privilege and His will to hold this GREAT SUPPER. Will you be there?