The image in the link complicates the poem as a whole. Since the title of it is “The Marriage of Heaven and Hell”, we are led to believe that the poem will end with the joining of Heaven with Hell. However, this particular page describes the coming of the “cherub with his flaming sword”, and, “when he does, the whole creation will be consumed”. This does not strike me as a happy resolution between Heaven and Hell.
The plate shows two male figures, one hovering above the other, who seems to be dead. To me, it is showing the cherub floating above a man who represents the death of Creation. However, the plate complicates the poem, because this is not clearly the interpretation that Blake wants us to have. The poem mentions fire, and so there is fire in the background of the plate. But if this cherub used to reside in the Garden of Eden, God’s Paradise, then why has it descended to Earth to destroy it with fire? The cause for this is an “improvement of sensual enjoyment”, which I interpret as sin. The complication for me, then, is why the guardian of the Tree of Life is also the one who will destroy the world in 6,000 years. The way this can be resolved, though, is if the cherub is the guardian of all things good, and by destroying a sinful Earth which has indulged in an “improvement of sensual enjoyment”, he is merely keeping preventing the spread of sin in his God’s creation.