Numbers 7:9

But unto the sons of Kohath he gave none, for the office that pertained to them was holy, and therefore they must bear upon shoulders.

Numbers 3:31

and their office was to keep the ark, the table, the candlestick and the altar, and the holy vessels to minister with, and the veil with all that served thereto.

2 Samuel 6:13

And ever, when they that bare the Ark of the LORD had gone six paces, he offered an ox and a fat sheep.

Numbers 4:4-16

even in the most holy place.

2 Samuel 6:6

And when they came to Nacon's threshing floor, Uzzah put his hand to the ark of God and held it, for the oxen stumbled.

1 Chronicles 15:3

And therefore David gathered all Israel to Jerusalem, to fetch the Ark of the LORD unto the place which he had ordained for it.

1 Chronicles 15:13

For because ye were not there at the first time, the LORD our God made a rent among us, for that we sought him not as the fashion ought to be."

1 Chronicles 23:26

Moreover, the Levites should now no more bear the tabernacle and all the vessels that pertain to the service thereof." -

Treasury of Scripture Knowledge

Summary

But unto the sons of Kohath he gave none: because the service of the sanctuary belonging unto them was that they should bear upon their shoulders.

Bible References

Because

Numbers 3:31
and their office was to keep the ark, the table, the candlestick and the altar, and the holy vessels to minister with, and the veil with all that served thereto.
Numbers 4:4
even in the most holy place.
2 Samuel 6:6
And when they came to Nacon's threshing floor, Uzzah put his hand to the ark of God and held it, for the oxen stumbled.
1 Chronicles 15:3
And therefore David gathered all Israel to Jerusalem, to fetch the Ark of the LORD unto the place which he had ordained for it.
1 Chronicles 23:26
Moreover, the Levites should now no more bear the tabernacle and all the vessels that pertain to the service thereof." -