Mars, God of War, was one of the lovers of Venus, Goddess of Love. Here Mars is asleep and unarmed, while Venus is awake and alert. The meaning of the picture is that love conquers war, or love conquers all. 
This work was probably a piece of bedroom furniture, perhaps a bedhead or piece of wainscoting, most probably the 'spalliera' or backboard from a chest or day bed. The wasps ('vespe' in Italian) at the top right suggest a link with the Vespucci family, though they may be no more than a symbol of the stings of love.
Mars is sleeping the 'little death' which comes after making love, and not even a trumpet in his ear will wake him. The little satyrs have stolen his lance - a joke to show that he is now disarmed.