The movement of the celebration
In the epiclesis, the Church asks the Father to send his Holy Spirit (or the power of his blessing) on the bread and wine, so that by his power they may become the body and blood of Jesus Christ and so that those who take part in the Eucharist may be one body and one spirit (some liturgical traditions put the epiclesis after the anamnesis).
In the institution narrative, the power of the words and the action of Christ, and the power of the Holy Spirit, make sacramentally present under the species of bread and wine Christ's body and blood, his sacrifice offered on the cross once for all.
Source: Catechism of the Catholic Church (Vatican.va)