4but not the Heptateuch or Books of Kings, because it will not be good for those of weak understanding to hear these writings at that hour; they should be read at other times.The Heptateuch (etymologically the "seven containers") is the name for the first seven books of the Hebrew Bible: Genesis, Exodus, Leviticus, Numbers, Deuteronomy, Joshua and Judges. To this list Benedict adds 1-2 Kings. Benedict suggests that these books not be read before bedtime.
I think it has to do with the sex in those books. My hunch is that Benedict doesn't want the monks reading some of those erotic stories before bedtime.