Concerning him (eis auton). Peter interprets Psa 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 Act 13:36 make it the Messiah. David is giving his own experience which is typical of the Messiah (Knowling).
I beheld (proorōmēn). Imperfect middle without augment of prooraō, common verb, but only twice in the N.T., to see beforehand (Act 21:29) or to see right before one as here. This idea of prȯ is made plainer by “before my face” (enōpion mou).
On my right hand (ek dexin mou). The Lord Jehovah like a defender or advocate stands at David’s right hand as in trials in court (Psa 109:31).
That (hina) here is almost result.
Moved (saleuthō). First aorist passive subjunctive of saleuō, to shake like an earthquake.