At the end of the Last Supper, the Lord Jesus prayed aloud to the Father.
He prayed for Himself, for His Apostles, and for us. In other words, He prayed as a priest. He offered Himself to the Father, He consecrated Himself, and He invoked divine assistance upon all the people gathered around Him—gathered around Him then and throughout the ages, from St. John and St. Peter down through time to us.
In the eternal Trinity–the blessed communion of the Father, Son, and Holy Spirit–there is no need for a priest. The three divine Persons are bound together in perfect, perpetual unity—more inseparable than a ball and its roundness or water and its wetness. A ball doesn’t need a priest to be round; water doesn’t need a priest to be wet; the eternal Son doesn’t need a priest to be consubstantial with the eternal Father.
But then God created. He created something other than Himself. He brought into existence a world with limts.
Don’t get me wrong. The world excites our wonder and esteem. As Woody Allen put it, “The world is the only place where you can get a good steak.” In this lovely world, you can grow blueberries; you can go for a boatride; you can listen to Mozart.