And to the priests that were reckoned in the households of their fathers from twenty years and above, to wait when their courses came.

These are the children of Levi in the households of their fathers the ancient heads, viewed and numbered by name and poll by poll from twenty year and above, to work in the service of the house of the LORD.

But at the last commandment of David, the Levites were numbered from twenty years and above -

"Number the children of Levi in the houses of their fathers and kindreds, all that are males from a month old and above."

And the sons of Merari in their kindreds were Mahli and Mushi. These are the kindreds of Levi in the houses of their fathers.

all that were able to war - for to do the work in the tabernacle of witness:

And the sons of Gershon were numbered in their kindreds and in the houses of their fathers,

And the kindreds of the sons of Merari were numbered in their kindreds and in the houses of their fathers,

The whole sum which Moses, Aaron, and the lords of Israel numbered among the Levites in their kindreds and households of their fathers -

"This shall be the manner of the Levites: from twenty five years upward they shall go in to wait upon the service in the tabernacle of witness,

"Speak unto the children of Israel and take of them, for every principal house, a rod, of their princes over the houses of their fathers: even twelve rods, and write every man's name upon his rod.

The rest of the sons of Levi: of the sons of Amram, Shubael. Of the sons of Shubael, Jehdiah.

And Hezekiah set the priests and the Levites in their order to wait by course, every man according to his office whether priest or Levite, for the burnt offerings and peace offerings, and to minister and to thank and to pray in the gates of the lodge of the LORD.

And these went up also: Telmelah, Telharsha, Cherub, Addan, and Immer; but they could not show their father's house, nor their seed, whether they were of Israel.

Treasury of Scripture Knowledge

Summary

Both to the genealogy of the priests by the house of their fathers, and the Levites from twenty years old and upward, in their charges by their courses;

Bible References

Genealogy

"Number the children of Levi in the houses of their fathers and kindreds, all that are males from a month old and above."
And the sons of Gershon were numbered in their kindreds and in the houses of their fathers,
"Speak unto the children of Israel and take of them, for every principal house, a rod, of their princes over the houses of their fathers: even twelve rods, and write every man's name upon his rod.
And these went up also: Telmelah, Telharsha, Cherub, Addan, and Immer; but they could not show their father's house, nor their seed, whether they were of Israel.

Twenty

all that were able to war - for to do the work in the tabernacle of witness:
"This shall be the manner of the Levites: from twenty five years upward they shall go in to wait upon the service in the tabernacle of witness,
These are the children of Levi in the households of their fathers the ancient heads, viewed and numbered by name and poll by poll from twenty year and above, to work in the service of the house of the LORD.

By their courses

And Hezekiah set the priests and the Levites in their order to wait by course, every man according to his office whether priest or Levite, for the burnt offerings and peace offerings, and to minister and to thank and to pray in the gates of the lodge of the LORD.
The rest of the sons of Levi: of the sons of Amram, Shubael. Of the sons of Shubael, Jehdiah.
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