When I first came across this image of Michael slaying the demon in the Bern Historical Museum, it really impressed me. That was long before I thought about any of the symbolism. I think I just admired it because of the contrasting beauty of the angel and gruesomeness of the demon.
It's a different concept from Egyptian and perhaps other cultures' symbolism of weighing of souls with scales (hardly a rare theme). The Egyptian Ma'at, for example, weighs the soul against a feather. Therefore, you would desire to have a light soul, unburdened by sins. Why then does the demon in this picture appear to be stepping into the scale? Would that not cause the soul to rise? I believe it's because here, the whole scale represents the individual--their virtues versus sins. If your virtuous self doesn't outweigh your sins, you get thrown to the crocodile. = P
The demon is definitely trying to 'tip the scales' in his own favor. Yet we have the power of God to protect and assist us. If God be for us, who can be against us? The figure in left basket is naked, to portray her innocence, like a pure and perfect Eve. She prays, and God (the Father) sends her a big bro to whup up on the demon who would waste her soul. Michael's face shows neither sorrow for the violence he commits in casting out evil, nor pleasure in destruction. He knows he carries the sword of justice and righteousness, not to achieve balance, rather to restore perfect goodness.
Blessed be Jah my rock who teaches my hands to wage war and my fingers to do the battle. My love, my fortress, my stronghold, my deliverer, my shield in whom I've taken refuge and the one who subdues my people under me. Oh Jah, what is man? Man is breath, his days are like passing shadow. Oh Lord, bow down thy heavens and descend, touch the mountains so that they smoke, flash forth the lightning and strike them, shoot forth thy arrows and confound them.--Ziggy Marley
And I will put enmity between thee and the woman, and between thy
seed and her seed; it shall bruise thy head, and thou shalt bruise
his heel.
And there was war in heaven: Michael and his angels fought against
the dragon; and the dragon fought and his angels, (8) And prevailed
not; neither was their place found any more in heaven. (9) And the
great dragon was cast out, that old serpent, called the Devil, and
Satan, which deceiveth the whole world: he was cast out into the
earth, and his angels were cast out with him. (10) And I heard a loud
voice saying in heaven, Now is come salvation, and strength, and the
kingdom of our God, and the power of his Christ: for the accuser of
our brethren is cast down, which accused them before our God day and
night.
http://www.moonchild.ch/Tarot/major/Justice/11extra.html