. . where the heart of the deceased is weighed against a feather - and must balance.

The heart represents the life and soul of the deceased and the feather represents the natural law (for your kind of being - human here on Earth, we presume).

If you've been a real jerk meanie you're obviously going to be way off ballance - but if you've been an super-pious do-godder shit you're also likely to be off balance and holding an appointment with the Eater of the Dead (a crocodile / hippopotamus critter with an eager expression).

You're supposed to live well and do good, but aren't held up to some standard of divine perfection - not in this lifeform, anyway, 'cause it ain't possible.