A Virgin Woman
...in keeping with a long-established divine pattern emphasizing the monergistic activity of God in redemptive history, a ‘barren’ woman is made fruitful (cf. Gn. 17:15-19; 18:9-14; Jdg. 13:1-24; 1 Sa. 1:1-20; Is. 32:15). Indeed, here we meet the climactic illustration of this principle. When the Spirit comes to mark the dawning of the new messianic era, not merely a barren woman, but a virgin woman, is with child (Is. 7:14; Mt. 1:23).
Sinclair Ferguson, The Holy Spirit, ed. Gerald Bray, Contours of Christian Theology (Downers Grove, IL: InterVarsity Press, 1996), 38.