Hebrews 7:23

There have been many priests. This is because they have been prevented from continuing by death.

1 Chronicles 6:3-14

The children of Amram: Aaron, Moses and Miriam. The sons of Aaron: Nadab, Abihu, Eleazar and Ithamar.

Nehemiah 12:10-11

Jeshua was the father of Joiakim, and Joiakim was the father of Eliashib, and Eliashib was the father of Joiada,

Hebrews 7:8

In this instance mortal men receive tithes, in the other by the one of whom it is testified that he lives.

Treasury of Scripture Knowledge

Summary

And they truly were many priests, because they were not suffered to continue by reason of death:

General references

Bible References

Were

Hebrews 7:8
In this instance mortal men receive tithes, in the other by the one of whom it is testified that he lives.
1 Chronicles 6:3
The children of Amram: Aaron, Moses and Miriam. The sons of Aaron: Nadab, Abihu, Eleazar and Ithamar.
Nehemiah 12:10
Jeshua was the father of Joiakim, and Joiakim was the father of Eliashib, and Eliashib was the father of Joiada,

General references

Numbers 20:26
Remove Aaron's priestly robes and put them on Eleazar. Aaron is going to die there.
Zechariah 1:5
Your fathers, where are they?' The prophets, do they live forever?