Right before the prayers of consecration, the Priest asks Almighty God, that He pie down His Holy Spirit upon the gifts and offerings. This outpouring is the Epiclesis. It was first by the power of the Holy Spirit that the Word was made flesh, as the Spirit came down upon the Virgin Mary. So, we recognize that is is not by the power or any other quality of the Priest that he turns the bread and wine into the body and blood of Christ. In some traditions and forms of the Liturgy, the Priest will breathe over the species, as a sign of the Spirit, and recollection that it is the Spirit dwelling in Him at work.