A.T. Robertson Commentary 2 Peter 1:21

"For no prophecy ever came by the will of man: but men spake from God, being moved by the Holy Spirit." — 2 Peter 1:21 (ASV)

For (γαρ). The reason for the previous statement that no prophet starts a prophecy himself. He is not a self-starter.

Came (ηνεχθη). First aorist passive indicative of φερω (verses 17f.).

By the will of man (θεληματ ανθρωπου). Instrumental case of θελημα. Prophecy is of divine origin, not of one's private origination (ιδιας επιλυσεως).

Moved by the Holy Ghost (υπο πνευματος αγιου φερομενο). Present passive participle of φερω, moved from time to time. There they "spoke from God." Peter is not here warning against personal interpretation of prophecy as the Roman Catholics say, but against the folly of upstart prophets with no impulse from God.