I heard another from the altar saying
Probably the angel which officiated at the altar and offered the prayers of the saints (Rev. Rev. 8:3-4+ cf. Rev. Rev. 14:18+) including those of the martyrs John saw under the altar following the opening of the fifth seal (Rev. Rev. 6:9+). He is in agreement with giving the earth dwellers blood to drink, for he attends the altar where the martyrs cry for vengeance. They are among those whose blood was shed. The NU and MT texts omit another. The Altar is either personified (for the prayers of the saints are upon it; and the martyrs are beneath it); or the words [the angel of] the Altar must be supplied.1
true and righteous are Your judgments
Gods righteous judgment is seen in His patient interaction with Abraham prior to the destruction of Sodom and Gomorrah where Abraham questioned God. Shall not the Judge of all the earth do right? (Gen. Gen. 18:25). Rather than being a blasphemous questioning of Gods inscrutable will, the passage serves as an intentional illustration of His just nature and righteous judgment. Not only are the Fathers judgments true and righteous during the pouring forth of the seven bowls, but upon the commencement of the Millennial Kingdom, the Sons rule will be the same:
Of the increase of His government and peace There will be no end, upon the throne of David and over His kingdom, to order it and establish it with judgment and justice from that time forward, even forever. The zeal of the LORD of hosts will perform this. (Isa. Isa. 9:7)The righteous nature of Gods judgment is taken up by Paul in his argument defending the sovereignty of God in election (Rom. Rom. 9:14-24). In fact, Gods judgment is required by His righteousness (2Th. 2Th. 1:6), for if He were to forever delay judgment, then He would be in violation of His own righteous nature. For God to forego judgment when it is due is as impossible as it is for the Holy One to lie.