I have seen the Scripture in the Old or New Testament which states that the priesthood is to be given to all men. However, I don't remember where I found it. Would you please help us to locate it?
"Therefore, if perfection were through the Levitical priesthood (for under it the people received the law), what further need was there that another priest should rise according to the order of Melchizedek, and not be called according to the order of Aaron? For the priesthood being changed, of necessity there is also a change of the law" (Hebrews 7:11-12)
"Coming to Him as to a living stone, rejected indeed by men, but chosen by God and precious, you also, as living stones, are being built up a spiritual house, a holy priesthood, to offer up spiritual sacrifices acceptable to God through Jesus Christ. ... But you are a chosen generation, a royal priesthood, a holy nation, His own special people, that you may proclaim the praises of Him who called you out of darkness into His marvelous light; who once were not a people but are now the people of God, who had not obtained mercy but now have obtained mercy" (I Peter 2:4-5, 9-10).
With the change in covenants came a change in the priesthood. Under the Old Testament, the priesthood was restricted to descendants of Aaron. Under the New Testament, the priesthood is given to every Christian. This is not a broad as "all men" that you thought you remembered, but it does mean that Christians, who come from every nation, serve God as priests -- offering up worship to God. Our priesthood is the reason we can approach God directly instead of searching out intermediaries.