Unto which (Tini). "To which individual angel." As a class angels are called sons of God (Elohim) ( Psalms 29:1 ), but no single angel is called God's Son like the Messiah in Psalms 2:7 . Dods takes "have I begotten thee" (gegennhka se, perfect active indicative of gennaw) to refer to the resurrection and ascension while others refer it to the incarnation. And again (kai palin). This quotation is from 2 Samuel 7:14 . Note the use of ei in the predicate with the sense of "as" like the Hebrew (LXX idiom), not preserved in the English. See Matthew 19:5 ; Luke 2:34 . Like Old English "to" or "for." See 2 Corinthians 6:18 ; Revelation 21:7 for the same passage applied to relation between God and Christians while here it is treated as Messianic.