...but where does it list the significance and use of the levels for the Imperial Fists Primarch's curse as listed in Rites of Battle.

It has three ranks and I have no idea what the significance and implementation of those ranks is.

Thanks.

Fear and Damnation section in the core rulebook. Don't worry, you're not the first to not have found it.

Alex

Thanks Alex, I was drawing a total blank.

Damned warpstone. Really need to quit heating my coffee with it.