1:20 first. This should read, “first of all” or “as of primary importance.”

1:20 prophecy. “Prophecy” refers not just to predictions of the future, but to any divinely inspired utterance—therefore to all the Holy Scriptures.

1:20 private interpretation. The meaning here is that no true prophecy springs forth from the private reasoning of the man speaking or writing. He may or may not understand the meaning and intent of his writing in terms of his own current situation, but its ultimate meaning involves far more than that. This would especially be true for Messianic predictions (note I Peter 1:10-12), but also applies to “all Scripture…given by inspiration of God” (II Timothy 3:16-17).

1:21 spake. Note also Hebrews 1:1.

1:21 moved. Compare Genesis 1:2. “The Spirit of God moved” in the presence of the primeval waters of the newly created cosmos, and it became vibrant with pulsating energy and activity. In somewhat analogous fashion, the Spirit of God moved the hearts, minds and pens of the holy (that is, called and set apart) men of God, and the Scriptures were formed, proceeding from the eternal mind of God to be revealed to His creatures.