Why is the priest only one who can drink wine and not the believers at Mass?
The Council of Trent taught that when we receive either the host or from the chalice we are receiving the fullness of Jesus’ body, blood, soul, and divinity. Receiving both species is not required to receive the fullness of the sacrament.
It is not a matter of the priest being the only one who can drink from the chalice. The faithful normally do not receive from the chalice because it is not necessary and because many parishes are not designed in a way that permits for orderly and smooth reception of both species.