That is, carnal knowledge. Mary could speak as a pure maiden, affirming her virginity (see on Matt. 1:23). Her manner of expressing this fact is the common Hebrew idiom for premarital chastity (see Gen. 19:8; Judges 11:39; etc.). As He so often does with us today, God first let Mary become fully conscious of the fact that the anticipated event was beyond human power, that it was impossible from man‘s point of view, before presenting to her the means by which it would be brought about. It is thus that God leads us to appreciate His goodness and His power and teaches us to have confidence in Him and in His promises.

 The attempt to read a vow of perpetual virginity into these words of mary is altogether unwarranted (see on Matt. 1:25). To remain thus a virgin in perpetuity was generally considered a reproach by the Jews, not a virtue. Inability to bear children was ever the occasion of chagrin and remorse on the part of a wife (see Gen. 30:1; 1 Sam. 1:4-7; etc.). The idea that she remained ever a virgin arose in later centuries, probably from a perverted sense of what constitutes virtue. It implies that the home, a divinely ordained institution, does not represent the highest ideal of social life. See on Matt. 19:3-12.

The context implies that Mary believed the angel‘s announcement unhesitatingly. In simple faith Mary asked how the coming miracle would take place.