Exodus 19:6
4 ‘You yourselves have seen what I did to Egypt and how I lifted you on eagles’ wings and brought you to myself. 5 And now, if you will diligently listen to me and keep my covenant, then you will be my special possession out of all the nations, for all the earth is mine, 6 and you will be to me a kingdom of priests and a holy nation.’ These are the words that you will speak to the Israelites.” 7 So Moses came and summoned the elders of Israel. He set before them all these words that the Lord had commanded him, 8 and all the people answered together, “All that the Lord has commanded we will do!” So Moses brought the words of the people back to the Lord.
Numbers 16:3
1 Now Korah son of Izhar, the son of Kohath, the son of Levi, and Dathan and Abiram, the sons of Eliab, and On son of Peleth, who were Reubenites, took men 2 and rebelled against Moses, along with some of the Israelites, 250 leaders of the community, chosen from the assembly, famous men. 3 And they assembled against Moses and Aaron, saying to them, “You take too much upon yourselves, seeing that the whole community is holy, every one of them, and the Lord is among them. Why then do you exalt yourselves above the community of the Lord?” 4 When Moses heard it he fell down with his face to the ground. 5 Then he said to Korah and to all his company, “In the morning the Lord will make known who are his, and who is holy. He will cause that person to approach him; the person he has chosen he will cause to approach him.
Notes and References
"... Here, therefore, right at the outset, we must differentiate between two possible applications of 'kingdom of priests:' it can serve as a slogan for setting the Jews above the Gentiles (or for the former's 'mission' vis a vis the latter), but it can also be used to militate against the notion that, within the Jewish people, some (Aaronites) are more priestly than others. Thus, even if Isaiah 61:6 reflects Exodus 19:6, it does not supply any support for the inner-Jewish application of the verse - which is the one so often ascribed to the Pharisees and the rabbis.' The idea of a common priesthood of all Israelites is clearly stated in another verse (although without echoing Exodus 19:6): 'For the whole congregation is holy and God is in their midst, so why do you [Moses and Aaron, Levite and priest] hold yourselves above the community of God?' (Numbers 16:3). True, there is no claim of common priesthood, but only of common holiness, but from Moses' answer (verse 10) it becomes clear that there was also a demand for priesthood; the same follows also from the end of the story (17:5). But with all due respect to some scholars to be cited in Part II, the Korah story could not possibly serve as a support for any Jew in the Second Temple period who wished to demand that all Jews be considered priests,' for the biblical story clearly and totally condemns the demand ..."
Schwartz, Daniel R. Studies in the Jewish Background of Christianity (p. 58) J. C. B. Mohr, 1992