Numbers 4:20

but they shall not go in to see the sanctuary even for a moment, lest they die."

Exodus 19:21

Yahweh said to Moses, "Go down, warn the people, lest they break through to Yahweh to gaze, and many of them perish.

1 Samuel 6:19

He struck of the men of Beth Shemesh, because they had looked into the ark of Yahweh, he struck of the people fifty thousand seventy men; and the people mourned, because Yahweh had struck the people with a great slaughter.

Leviticus 10:2

And fire came forth from before Yahweh, and devoured them, and they died before Yahweh.

Numbers 4:15

"When Aaron and his sons have finished covering the sanctuary, and all the furniture of the sanctuary, as the camp moves forward; after that, the sons of Kohath shall come to carry it: but they shall not touch the sanctuary, lest they die. These things are the burden of the sons of Kohath in the Tent of Meeting.

Numbers 4:19

but thus do to them, that they may live, and not die, when they approach to the most holy things: Aaron and his sons shall go in, and appoint them everyone to his service and to his burden;

Hebrews 10:19-20

Having therefore, brothers, boldness to enter into the holy place by the blood of Jesus,

Revelation 11:19

God's temple that is in heaven was opened, and the ark of the Lord's covenant was seen in his temple. Lightnings, sounds, thunders, an earthquake, and great hail followed.

Treasury of Scripture Knowledge

Summary

But they shall not go in to see when the holy things are covered, lest they die.

Bible References

They shall

Numbers 4:15
"When Aaron and his sons have finished covering the sanctuary, and all the furniture of the sanctuary, as the camp moves forward; after that, the sons of Kohath shall come to carry it: but they shall not touch the sanctuary, lest they die. These things are the burden of the sons of Kohath in the Tent of Meeting.
Exodus 19:21
Yahweh said to Moses, "Go down, warn the people, lest they break through to Yahweh to gaze, and many of them perish.
Leviticus 10:2
And fire came forth from before Yahweh, and devoured them, and they died before Yahweh.
1 Samuel 6:19
He struck of the men of Beth Shemesh, because they had looked into the ark of Yahweh, he struck of the people fifty thousand seventy men; and the people mourned, because Yahweh had struck the people with a great slaughter.
Hebrews 10:19
Having therefore, brothers, boldness to enter into the holy place by the blood of Jesus,
Revelation 11:19
God's temple that is in heaven was opened, and the ark of the Lord's covenant was seen in his temple. Lightnings, sounds, thunders, an earthquake, and great hail followed.