Alma 13:7

this High Priesthood being after the order of his Son, which order was from the foundation of the world; or in other words, being without beginning of days or end of years, being prepared from eternity to all eternity, according to his foreknowledge of all things.

This high priesthood followed the order of God’s Son. This order was from the very beginning of the world. In other words, it has no beginning or end. It was prepared from forever to forever, because God knew all things ahead of time.

This high priesthood follows the pattern of his Son—an order that has existed since before the world began. In other words, it has no beginning and no end. It was prepared from eternity to eternity, according to God’s knowledge of all things.