1 Peter 2:9
But you are a chosen race, a royal priesthood, a holy nation, God's own people, that you may declare the wonderful deeds of him who called you out of darkness into his marvelous light.
Many people fancy that St. Peter, in writing these words, is saying "Under the Old Covenant, only a special class called the Levites were priests, while everybody else was just a slob but now, with the New Covenant everybody is a priest." Since they take St. Peter to be saying this, they therefore assume that there is no need for a special sacerdotal priest in the New Covenant and suppose that the Catholic priest is just some sort of Dark Ages blunder. But this is to misread the text. For St. Peter is quoting the Old Testament (Exodus 19:6). Israel, as much as the Church was a "kingdom of priests". Yet this priestly nation of Israel still had a specially ordained office of priests among it, ministering to the people. All the New Covenant does is continue this pattern of a priestly people (that'd be you and me) who are themselves served by a special office of priests among us. We are priests by our baptism (as well as prophets and kings). Similarly, we are all married in our baptism (to Christ the Groom while we are member of his Bride, the Church). But this does not mean that we cannot celebrate a special sacrament of Marriage. Nor does it mean that God cannot call certain men among us to be specially ordain servants of the sacraments. That is, in fact, precisely what he does–for our good. Today, thank God for his ordained priests and for your baptismal priesthood!