Focus on Mercury and Argus (Jordaens) and analyze the Background story.
The painting depicts a scene from the myth of Mercury, Argus (Argos) and Io as told in The Metamorphoses written by Ovid (I, 583 ; IX, 687). In the story Jupiter (Zeus) has fallen in love with Io, a priestess of Hera, his wife, who quickly discovers the affair. Jupiter transforms himself into a bull and transforms Io into a beautiful, white heifer in order to hide from Hera's wrath. Hera sees through this scheme and demands the heifer as a present. To end their affair, Hera puts Io under the guard of the giant Argus Panoptes, who has 100 eyes. Jupiter commands his son Mercury (Hermes) to set Io free by lulling Argus to sleep with an enchanted flute. Mercury, disguised as a shepherd, is invited by Argus to his camp. Mercury charms him with lullabies and then cuts his head off.Jordaens depicts in the picture the moment when Mercury stealthily picks up his sword to murder the sleeping Argus.  The protagonists of the fable are not shown in their divine condition. He has turned Argus into a tired and shaggy old man who does not have 100 eyes and has lost his frightening aspect. Mercury is a simple shepherd with dirty feet who has just numbed Argus' vigilance by playing a flute which is lying on the ground.
Argus Panoptes Hermes Argus The Metamorphoses Jupiter Hera Ovid Io Mercury Jordaens Zeus Metamorphoses