Charles Ellicott Commentary Revelation 16:5

"And I heard the angel of the waters saying, Righteous art thou, who art and who wast, thou Holy One, because thou didst thus judge:" — Revelation 16:5 (ASV)

And I heard the angel of the waters...—That is, the angel who was set over the waters, or the angel who is, on the heavenly side, representative of the waters. (See Excursus A: On the Angels.) The angel acknowledges God’s righteousness. You are righteous... because You judged these things—i.e., because of the righteous law which these judgments manifested.

On verses 5-7:

But this state of things is declared to be a just retribution, and reasonably so; for the corruption arises because the true power of life has been rejected: it is the refusal of the good, the lack of the life-giving element, which is the secret of all death, physical, moral, spiritual.

“It is life we want when breath is scarce.” The world-power and its worshippers have driven away goodness and faith, the elements of the higher life of man; they have slain the just and the righteous, who were the salt of the earth; they have rejected Christ, who is the life of men; how can they reap anything but decay and death?

They slay the righteous; the death of righteousness leaves them nothing but the lifeless blood behind. They can no longer drink moral life from the good; there is only the legacy of death. Blood of saints and prophets they poured out; and blood You gave them to drink.