Commentary on the Apocalypse and commentary on the Book of Daniel
Purchased by J. Pierpont Morgan (1837-1913) in 1910
Apocalypse: Angels of Plagues (Revelation 15:1) -- Seven nimbed angels holding vials.
Apocalypse: Song of Moses and Lamb (Revelation 15:2-4) -- Lamb of God cross-nimbed, holding cross-staff, flanked by six nimbed saints playing musical instruments; sea of glass; inscriptions UBI [TENENTES] CITHARAS [ET CANTANTES] CANTICUM [NOUU]M MAGNUM and (ET UIDI) HOMINES TENENTES [...] ANTE AGNUM ET MARE UIR[...].
And I saw another sign in heaven, great and wondrous: seven angels holding the seven last afflictions. For with them, the wrath of God is completed. And I saw something like a sea of glass mixed with fire. And those who had overcome the beast and his image and the number of his name, were standing upon the sea of glass, holding the harps of God, and singing the canticle of Moses and the canticle of the Lamb, saying: "Great and wondrous are your works, Lord God Almighty. Just and true are your ways, King of all ages." (Rev. 15:1–3)
According to the commentary, the seven angels are the seven churches of Asia, who will empty their cups (shown as flasks) on the blind so that they might see the truth. In the second register the successful believers praise the Lamb (here holding a cross), but with bow instruments rather than harps. The wavy purple band at bottom represents the sea of glass.