The natural guess, to a person from a modern Judeo-Christian background, would be wrongdoing of whatever sort the Egyptian religion defined. But we also say in English that a person with guilt or worry - deserved or otherwise - has a "heavy heart", that happy, carefree people - for cause or otherwise - have "light hearts", and that decisions can "weigh on" a person both before and after they are made. It seems unlikely that's what the Egyptians meant, but it highlights the ambiguity of the expression, and its ability to foster rich metaphorical language.
So please, historians, what did the Egyptians mean by this story?
At last! An AskHistorians question I know something about!
The feather was symbolic of maat, the Egyptian concept of order. Maat was also a goddess with feathers on her head, and so the weighing of the heart was to ascertain whether you has committed any actions against order. Luckily, due to the funerary procedure- we do have a pretty good idea what these were!
This was the Negative Confession, an important stage in which the deceased listed the actions they hadn’t done, and it corresponds to Spell 125 in the Book of the Dead. For one version of the full spell you can go to UCL’s website here - (there is another version here I'm a little reluctant to link it as Tour Egypt isn't an Academic website- however I have always found it reliable, so it is certainly worth checking out!)
Anyway, I have chosen a selection from UCL,
As you can see some of them will seem familiar to a western audience, I am sure I have read a version which mentioned murder, but I can’t seem to find it at the moment. Others are particularly relevant to the Egyptian experience- the Egyptians considered it dreadful to disturb offerings, and damming a the river when the society relied on the annual inundation was a serious offense.
Obviously, we can't know for certain exactly how the Egyptians interpreted their afterlife. But we have every reason to believe they took the weighing of the heart as a literal ceremony- that was undergone by the deceased's spirit. Many texts, and versions of the Book of the Dead, represent the funeral, aswell as the afterlife and the weighing of the heart ceremony. As we believe the funeral is depicted accurately based on archaeological evidence- it makes sense the Egyptians believed the afterlife was also accurately shown. The spells in the Book of the Dead could be read by the spirit as it entered the afterlife- and Spell 125 made sure the deceased said the correct thing to Anubis, and stopped their heart being eaten!
Anyway, I hope this is useful, and if you have anymore questions I will help the best I can!
Sources:
Assmann, J. 2001. Death and Salvation in Ancient Egypt
Taylor, J. 2010. Journey through the Afterlife
Taylor, J. 2001. Death and the Afterlife in Ancient Egypt