Luke wrote this Gospel so «that you [Theophilus] may have certainty concerning the things you have been taught [i.e., catechesis]» (1:4). It proceeds with a barrage of questions. The first comes from Zechariah: «How shall I know?» (1:18). This is a question of knowledge. The angel Gabriel answers that we shall know by the word of God (1:19). The second comes from Mary: «How will this be?» (1:34). This is a question of agency, of how the Son of God can become human. Gabriel answers that it will...