Holy Spirit: The priest blesses with the authority of God. On behalf of God. The blessing of the priest is the blessing of Christ. If the priest blesses the union of two people, it becomes a marriage because the power of the priest is the power of God. Whatever the priest binds on Earth is bound in Heaven. The blessing of the priest has an eternal power and value; it commits reality to yield to the will of God.
The blessing of lay people draws only from the blessing of the priest, because the blessing of the priest comes directly from God, and the blessing of lay people is its derivative. The graces flowing from the cross are granted to mankind through the mediation of priests. The cross is a force and an exorcism in itself, so making it with faith always brings its blessing upon the world, upon specific persons or matters. This is why parents should bless children, spouses should bless each other. You should bless people, food, animals, rooms, sick places in the body. You do not use directly the power of Christ through this, but you draw from the redemptive grace of the cross of Christ.
The difference in the blessing of a priest and a layman is such as the difference between Christ and His cross. In the first case, Christ Himself blesses, and in the second the blessing flows from the cross upon the power of the redemptive sacrifice of Christ, which sanctified the cross.
Translated from: Życie sakramentalne pierwotnego Kościoła według św. Agnieszki, na podstawie Orędzi na Czasy Ostateczne które własnie nadeszły, Grzechynia 2017, p. 86-87