Then said Mary unto the angel, How shall this be, seeing I know not a
man?
Since the
time of Augustine (Of Holy Virginity, 3), many have interpreted this verse as
evidence that Mary, prior to the Annunciation, took a vow of perpetual
virginity. Some commentators ask, why would Mary ask a question like this,
using the present tense, if she planned on having normal sexual activity upon
marrying Joseph, to whom she was espoused? However, this is reading too much into the use of the present tense of Luke 1:34.
On pages
532-33 of his book, Greek Grammar Beyond the Basics, Daniel Wallace
provides a discussion of the "Perfective Present," wherein the
present tense may be used to emphasise the results of a past action that are
still continuing; in Luke 1:34, this would refer to Mary being at the time of
the Annunciation, a virgin; there is no grammatical justification to read into
this verse a vow of life-long virginity (especially in light of texts that
speak of "brothers" and "sisters" of Jesus, for e.g.).
As we read in Wallace's (ibid. p. 532):
There are two types: one lexical, the other contextual. The lexical type involves certain words (most notably ηχω, which almost always has a perfective force to it). The other type is contextual. This use of the present is especially frequent with λεγει as an introduction to and OT quotation. Its usual force seems to be that although the statement was spoken in the past, it still speaks today and is binding on the hearers.
Other
instances of this "perfective present" in the Greek New Testament
include:
But they have not all obeyed the gospel, for Esaias saith (λεγει), Lord, who hath believed our report? (Rom
10:16)
Wherefore he saith (λεγει), When he
ascended up on high, he led captivity captive, and gave gifts unto men. (Eph
4:8)
For the scripture saith (λεγει),
Thou shalt not muzzle the ox that treateth out the corn. And, The labourer is
worthy of his reward. (1 Tim 5:18)
And we know that the Son of God is
come (ηχει) . . . (1 John 5:20)
In this light, all that Luke 1:34 says is, at the time of the visitation of Gabriel, Mary was a virgin; there is no exegetical warrant to read into her words as evidence of a previous vow of perptual virginity; instead, it simply reflects Mary thinking Gabriel meant that she would get pregnant, prior to "coming together" with Joseph (cf. Matt 1:18, 25) at the time of the angelic announcement.
For another discussion of this verse, see John McHugh, The Mother of Jesus in the New Testament (New York: Doubleday, 1975), 200-254.