In Ancient Egypt, the feather was a symbol of Ma'at. Ma'at was a goddess that was loved and feared simultaneously--for she represented truth, morality, and justice. Egyptians admired Ma'at for her ability to do the right thing, but that didn't stop people from worrying about the fateful day when they would come face-to-face with the goddess.
While newly deceased souls waited in limbo, it was Ma'at who delivered their fate. Ma'at would place her feather on one side of a scale, and the person's heart on the other. If the heart weighed more than the feather, it was a sign that it was heavy with sin. The soul would be rejected and unable to enter the utopian afterlife waiting just beyond the veil.