Ask an OBGYN about Mary’s virginity and you might get a clinical answer. Ask many theologians and they’ll likely talk about Jesus’s lack of an earthly father and Original Sin. Ask most people on the street and they’ll scoff at that “puritanical fairy-tale.”

Now ask the New Testament author, Matthew. What’s his answer? He’s going to tell you a seemingly straightforward story in the first chapter of his gospel. In fact, it happens to be the reading in many churches this coming Sunday. Matthew’s narrative is excellent, but it’s far from complete. He spends more time winking than explicating.

Matthew does provide us, however, with an invaluable service: he sticks out his textual finger and points. He points us back, all the way back, to a prophet who’s brimming with answers. This guy’s name is Isaiah. He’s not only the Shakespeare of the prophets; he’s the man with the plan. Isaiah sits us down and tells us the reason Mary’s virginity was so crucial to the story of salvation. Though it’s right there in the Bible, it’s not the typical way we hear the virgin birth explained.

Mary’s virginity has to do with the story of a jackass king, two growling enemies, a young lady, and a big, bad dog.

The Jackass King and the Big, Bad Dog

In the 700’s BC, a jackass king named Ahaz ruled over Judah from the age of 20 to 36. Now when I say “jackass,” my apologies to the real beasts of burden. Ahaz was much worse. He murdered his own offspring in ritual sacrifice. He also robbed the temple’s treasury to buy the protection of Assyria, a country that makes our modern terrorist organizations look PG. And these are only a couple of the stains on Ahaz’s long and soiled rap sheet.

At a momentous point in Ahaz’s reign, he faced a crossroads. Two menacing foes were stalking his nation: the Arameans and the Israelites of the northern kingdom. Ahaz and his people were shaking like leaves in the wind (Isa. 7:2). They were doomed. Their only hope—so they thought—would be to whistle for the big, bad dog named Assyria to come greedily loping to their rescue. The downside? They’d be selling their soul to that godless nation.

But Isaiah has another plan. It’s very simple: trust God. Don’t trust your fear. Don’t trust military muscle. And damn sure don’t trust psychopathic Assyria. In one of the most memorable Hebrew wordplays in the Bible, the prophet tells Ahaz: “If you will not believe [ta-a-minu תַאֲמִינוּ], you shall not stand [te-a-menu תֵאָמֵנוּ (7:9". One might say, “trust or tumble; faith or fall.” These are your only two options.

But God’s not done. Our prodigal Lord offers Ahaz a propitious sign. He literally promises to move heaven and earth, if that what it takes for the king to trust him (7:11). “Name your sign, any sign, and I’ll do it,” the Lord says. But the royal jackass closes his eyes, his heart, his soul in a big fat hee-hawing No.

Why? It all seems too impossible for him. Ahaz sizes up his options. Superior forces are closing in around him. His enemies will squash his population, kill him, and stomp his land into a waste, a tohu vavohu like Genesis 1:2. Ahaz reasons to himself: “Our only real choice is the ordinary human way—to ally ourselves with someone, to covenant ourselves to Assyria. That’s the only conceivable hope we have.”

And, now, with that all as the setup, here comes what we’ve been waiting for.

The Same Old Story, Told in a New Way

When Ahaz refuses to believe the Lord, when he even rejects the offer of a sign, Isaiah responds, “Listen now, O house of David…The Lord himself will give you a sign. Behold, the virgin shall conceive and bear a son, and shall call his name Immanuel” (7:14). In the verses that follow, to the end of the chapter, Isaiah delivers a smackdown on Ahaz. The two kings he so fears will soon be decimated. And the Assyrian ally he has chosen—that big, bad dog—will turn and sink its fangs into him. His land that he was afraid would become a waste, will indeed become so, at the hands of the very Assyrians in whom he put his trust. The land of milk and honey will become a bramble of briars and thorns (7:24).

Oh, Ahaz, you have chosen poorly.

But let us go back to the virgin, the one whose mother will name her Miriam (in Hebrew) but whom we know better as Mary. Now we are ready finally to answer the question of why her virginity was so crucial.

We might it summarize like this: Ahaz surmised that the only conceivable hope he had was to turn to ordinary means for salvation, so God conceived hope in an extraordinary way by a virgin becoming pregnant with Salvation himself.

It’s really the same old story, just told in a fresh and even more miraculous way. Abraham and Sarah couldn’t conceive the promised son because they were too old, so God conceived the hope named Isaac in them in an extraordinary way. He was calling them to live by faith in his creative word (see Rom. 4:16-25). As it was for Abraham and Sarah, so it was for Isaac and Rebekah, Samuel’s parents, Samson’s parents, and John the Baptist’s parents. Into wombs that seemed unable to conceive, God caused conception to occur by the power of his vivifying word. All he wanted was for his people to live by faith in that word, which speaks life into death, light into darkness, hope into despair, a child into a womb that one would never expect to swaddle life.

Bedeviling Unbelief

I think we need to work Ahaz into all our Christmas pageants. Dress him as an arrogant king with a donkey tail and have him sulk over in the door with a stupid glare of incredulity on his face. The church, through the centuries, has confessed, “born of the virgin Mary” in the Creed, as an affront to that old king—and to all our own jackassing, Ahazing unbelief that still bedevils us.

Mary, according to everything we (think) we know, should not be able to get pregnant since she’s a virgin. But, of course, according to everything we (think) we know, the world should not come into existence just by God speaking; nor should a 90-year-old woman named Sarah conceive just because God promised; nor should the tiny nation of Judah be saved just because God says it will; nor should a boy born in Bethlehem be the Word of God incarnate, Immanuel, come to recreate us all, and, through his resurrection, to usher an unutterable hope into our lives.

But it’s all deliciously, crazily true because God’s word does what it says.
And he does it all for you.
That may not be your usual reason for the virgin birth, but it’s Isaiah’s.
And it’s good news for you from beginning to end.