{Of whom} (peri hou). Or "concerning which," for hou can
be either masculine or neuter (genitive). It is the likeness of
Jesus as high priest to Melchizedek that the author has in mind.
He is ready to discuss that but for the fear that the reader may
fail to grasp his meaning, for he will run counter to the usual
Jewish ideas. Hence he pauses to stir up the interest of the
readers ( 5:11-6:20 ) before going on with the argument
( 7:1-28 ). {Hard of interpretation} (duserm(886e)eutos). Late and
rare verbal compound (dus, herm(886e)eu(935c)), in Diodorus and Philo,
here only in N.T. Hard to explain because of the strange (to
Jews) line taken, but still more because of their dulness. {Dull
of hearing} (
(9374)hroi tais akoais). Old adjective (papyri also),
from negative 
(885c) and (9374)he(935c), to push, no push in the hearing,
slow and sluggish in mind as well as in the ears. In N.T. only
here and  6:12  (slack, sluggish). Plato calls some students

(9374)hroi (stupid).