By the mouth of our father David (tou patros hēmōn dia pneumatos hagiou stomatos Daueid). From Psa 2:1. here ascribed to David. Baumgarten suggests that the whole company sang the second Psalm and then Peter applied it to this emergency. The Greek MSS. do not have dia (by) here before stomatos, but only dia before pneumatos hagiou (the Holy Spirit). Hort calls this a “primitive error” perhaps due to an early scribe who omitted this second dia so close to the first dia (Robertson, Introduction to the Textual Criticism of the N.T., p. 238). A small list of such primitive errors is there given as suggested by Dr. Hort.
Why (hina tōi). This Greek idiom calls for genētai (second aorist middle subjunctive),
That what may happen.
The Gentiles (ethnē). So always in lxx, while laoi (peoples) can include Jews.
Did rage (ephruaxan). First aorist active indicative of phruassō, late word, to neigh like a horse, to prance or stamp the ground, to put on lofty airs. Only here in the N.T. in this quotation from Psa 2:1.
Imagine (emeletēsan). First aorist active indicative of meletaō. Old verb from meletē (care), to practise, to caution, as orators and rhetoricians. Only here in the N.T. in this quotation.