John Chrysostom — as excerpted in the Catena Aurea on Luke 1:26-27

“(sup. Mat. Hom. 4.) The angel announces the birth to the virgin not after the conception, lest she should be thereby too much troubled, but before the conception he addresses her, not in a dream, but standing by her in visible shape. For as great indeed were the tidings she receives, she needed before the issue of the event an extraordinary visible manifestation.”