Exegesis kathōs elalēsen ‘as he spoke’, subject God. dia stomatos tōn hagiōn aiōnos prophētōn autou ‘through the mouth of his holy prophets of old’. dia stomatos in Luke and Acts always (with the exception of Acts 15:7 where the reference is to the preaching of the Gospel) introduces a quotation of, or a reference to, a word of God in the Old Testament, cp. Acts 1:16, 4:25 (David) 3:18 (all the prophets). hagios ‘holy’ here as an attribute of people consecrated to God, cp. A-G s.v.
Luke 1:70