The “knowledge” intended is perhaps chiefly ritualistic and musical - such knowledge as enabled them to conduct the service of the sanctuary satisfactorily.
They did eat throughout the feast - literally, “they did eat the feast;” i. e. “they kept the feast,” which was essentially kept by the eating of unleavened bread. The Levites kept the feast during the full term appointed for it, never failing in their duties, but taking their part day after day, both in the sacrifice of the victims and in singing praises to God.