Concerning him (εις αυτον). Peter interprets Psalm 16:8-11 as written by David and with reference to the Messiah. There is but one speaker in this Psalm and both Peter here and Paul in Acts 13:36 make it the Messiah. David is giving his own experience which is typical of the Messiah (Knowling).

I beheld (προορωμην). Imperfect middle without augment of προοραω, common verb, but only twice in the N.T., to see beforehand (Acts 21:29) or to see right before one as here. This idea of προ- is made plainer by "before my face" (ενωπιον μου).

On my right hand (εκ δεξιων μου). The Lord Jehovah like a defender or advocate stands at David's right hand as in trials in court (Psalm 109:31).

That (ινα) here is almost result.

Moved (σαλευθω). First aorist passive subjunctive of σαλευω, to shake like an earthquake.