Speaking of the priesthood, Paul said; "And no man taketh this honor unto himself, but he that is called of God, as was Aaron." Hebrews 5:4
More recently, Joseph Smith said, as God's mouthpiece. "We believe man must be called of God, by prophecy, and by the laying on of hands by those who are in authority, to preach the Gospel and administer the ordinances thereof." Article of Faith 5
After the eternal order of the Son of God, the priesthood is an eternal power, which power is only present in the face of righteousness. Doctrine and Covenants 107:1-5; 84:17-22; 121:34-41
I am grateful for the power of the priesthood after experiencing many sacred and special healings and blessings. As with other gifts from God, faith is required to realize these things.