Still this text, Acts ii, 36, does not refer to the time of the Incarnation, but to that of the Resurrection. In the Resurrection, God gave to His Incarnate Son for the first time the full glory of Messiahship and Lordship, the glory of the Only-begotten (John i, 14), which was His by right, but was not actually enjoyed by Him, in the time of His voluntary kenosis (Phil. ii, 7), in the days of his flesh (Heb. v, 7). Similarly St Paul (Acts xiii, 32, 33) interprets the text, This day have I begotten thee (Ps. ii, 7), to mean, 'This day of thy resurrection have I shown thee forth for my Son.' -- An example from history. According to the maxim, 'The king never dies,' Charles II was king the instant his father's head fell, January 29, 1648: he came into possession of his kingdom when he entered London, May 29, 1660.
Of God and His Creatures: 4.4