Now therefore, if ye will obey my voice indeed, and keep my covenant, then ye shall be a peculiar treasure unto me above all people: for all the earth is mine. (Exo 19:5)
But ye are a chosen generation, a royal priesthood, an holy nation, a peculiar people; that ye should shew forth the praises of him who hath called you out of darkness into his marvelous light. (1 Pet 2:9)
Often, Evangelicals who reject the existence of a ministerial priesthood in the New Covenant, cite 1 Pet 2:9 as "proof" that all believers are part of the "priesthood of all believers," and that there is no New Covenant priest (except for Jesus). Of course, this ignores the biblical evidence for a New Covenant priesthood, such as the priestly language used in the Last Supper accounts as well as the prophecies of such a priesthood by Old Testament prophets, such as Isaiah and Jeremiah (see here for a discussion). Furthermore, the appeal to 1 Pet 2:9 to support this relatively late concept in Christian theology is based on eisegesis, as is so many of the doctrines Evangelical Protestants hold to (e.g., purely symbolic view of baptism; the Trinity; sola scriptura; forensic justification; eternal security).
Firstly, note that it is an established fact from Hebrews that Christ is the High Priest of the New Covenant, just as there was a High Priest (Aaron) in the Old Covenant (e.g., Heb 4:14). This shows us that not all priests are of the same rank, something inconsistent with the Evangelical claim. Secondly, we know that there was a Levitical priesthood that was of a lower rank than the High Priest but still superior in rank to the "priesthood of all believers" and thus one would be justified in expecting this second rank (members of an ordained, ministerial priesthood) of priests to be paralleled in the New Covenant along with the clear presence of the first (the great High Priest, Jesus) and third rank ("Royal Priesthood").
This is further substantiated by the fact that even after Moses calls the people a royal priesthood, he goes on to put them into different categories (those of priests and laity):
And the Lord said unto Moses, Go down and charge the people, lest they break through unto the Lord to gaze, and many of them perish. And let the priests also, which come near to the Lord, sanctify themselves, lest the Lord break forth upon them. And Moses said unto the Lord, The people cannot come up to mount Sinai: for thou chargedst us, saying, Set bounds about the mount and sanctify it. And the Lord said unto him, Away, get thee down, and thou shalt come up, thou, and Aaron with thee: but let not the priests and the people break through to come up unto the Lord, lest he break forth upon them. (Exo 19:21-24)
Clearly, there is a second class of priests, and these are members of a ministerial priesthood.
That the New Testament authors understood this correspondence between the Old and New Covenant priesthoods can be seen in Jude 11:
Woe to them! For they go the way of Cain, and abandon themselves to Balaam's error for the sake of gain, and perish in Korah's rebellion. (NRSV)
In this verse, Jude warns the Christian community to respect the priest-laity division, noting that there will be disobedient members of the community who will be modelled after Cain, Balaam, and Korah who engaged in such a rebellion. All these situations were sins involving the priesthood. Korah's rebellion, for instance, is the most noteworthy of the three; in Num 16 Korah, serving as an equivalent of a deacon, gets upset and gathers a group of friends and engages in a rebellion:
And they gathered themselves together against Moses and against Aaron, and said unto them, Ye take too much upon you, seeing all the congregation are holy, every one of them, and the Lord is among them: wherefore then lift ye up yourselves above the congregation of the Lord? (Num 16:3)
Moses then rebukes Korah and says to him that he would be thankful that he is a deacon, but that he should not seek to raise himself to the level of a priest:
And he hath brought thee near to him, and all thy brethren the sons of Levi with thee: and seek ye the priesthood also? (Num 16:10)
Funnily enough, Evangelicals would side with Korah on this! They would say to Latter-day Saints and others who hold to a ministerial priesthood in the New Covenant, "you raise yourself above everyone else; everyone is equal!"
The only way Jude's warning of a modern Korah-like rebellion makes any sense is if there will be Christians who will try to usurp authority and "move up" in the New Covenant priesthood--it makes no sense if the Evangelical understanding of the "priesthood of all believers" is correct.
As with so many of their beliefs and practices, Evangelicals are forced to defend a doctrine that is void of any sound biblical-exegetical support and is, in reality, based on a concept Martin Luther invented in 1520 in On the Babylonian Captivity of the Church. They are also in the unenviable position of holding to an ecclesiology and understanding of the "priesthood" that would result, if they were consistent, in the rejection of Isaiah and Jeremiah as false prophets as they prophesied of a ministerial priesthood as being part of the New Covenant (see the paper linked above).