The doctrine of the virgin birth is one of the foundations and central doctrines of true Christianity. Without it, Christ would be just a "mere man" and not the begotten Son of God. If he were anything short of literally God in the flesh, his death would not be able to atone for the sins of ALL humans who either did or would exist.
If Christ were brought into this world as the result of sex, the entire New Testament would be a LIE. This is why belief in a virgin birth is so critical. It is a unique Biblical miracle that testifies of his divine origin. It is a sign to all humans that God so LOVED his creation that he was willing to offer the greatest sacrifice he could in order that they may live forever (John 3:16 - 17).
Denying the miraculous
Most Christians, up until the nineteenth century, accepted the Virgin Birth without hesitation until liberal theology began to challenge the Bible's miracles and the divinity of Christ. Liberal theologians sought to reinterpret Jesus as nothing more than a wise man and good teacher who died in the first century A.D. They sought to cast doubt on the veracity of the Bible and the miracles it records.
Isaiah 7:14 is the only verse in the Old Testament where the miraculous conception and birth of man's Savior is predicted. As such, it is a prime target of liberal teachers seeking to discredit the claims concerning the miraculous appearance of man's Savior.
Behold, the virgin shall conceive and bear a Son, and shall call His name Immanuel (Isaiah 7:14, NKJV)
The focus of the attack against the supernatural conception of Christ centers on the translation of Isaiah 7:14. The Hebrew word translated "virgin" in the verse is almah (Strong's #H5959). Some have suggested that almah does not mean a young chaste woman. They state that Isaiah would have used the Hebrew word bethulah (Strong's #H1330) if he desired to unambiguously write about a young woman who never had sex.
The truth is that almah is the BEST word the prophet Isaiah could have chosen to convey the concept of virginity. There exists, in the Old Testament, no place where almah requires clarification before it can be translated as referencing a young female virgin of marriageable age. This is not the case with the word bethulah, which requires clarification.
16 Now the young woman was very beautiful to behold, a virgin (bethulah); no man had known her. And she went down to the well, filled her pitcher, and came up (Genesis 24:16, NKJV)
Notice that bethulah needs the clarification of "no man had known her" in order to be translated as "virgin."
43 behold, I stand by the well of water; and it shall come to pass that when the virgin (almah) comes out to draw water . . . (Genesis 24:43, NKJV)
Note that several verses away from where bethulah needed clarification for a correct translation that almah does not. Both verses speak of the same woman, Rebekah, whom God specially selected to be the wife of Isaac (Abraham's son).
Almah is used in only six other places in the Old Testament other than Isaiah 7:14. In all cases, it references a virgin or 'maid' who is at an age where she can be married. This is not the case with bethulah, which can refer to a married female (Joel 1:8). In Genesis 24:43, almah refers to Rebekah whom was chosen to be the wife of Isaac. In Exodus 2:8, it references Miriam who, at a young age, helped save her baby brother Moses from being killed. In Psalm 68:25, it refers to young virgin girls playing timbrels. In Song of Solomon 1:3 and 6:8, it is used in reference to young unmarried maidens. In Proverbs 30:19, it refers to the courtship of an unmarried maiden and a man.
What does the New Testament say?
Mary, while betrothed to Joseph, became pregnant with Jesus through the power of the Holy Spirit (Matthew 1:20, Luke 1:31, 34 - 35). An angel was sent to Joseph to tell him that Mary's condition did not come through sex but that she would give birth to Christ through a miracle from God (Matthew 1:20 - 21). Matthew then quotes Isaiah 7:14 regarding this supernatural event.
22. Now all this came to pass, that it might be fulfilled which was spoken by the Lord through the prophet (Isaiah), saying, 23. "Behold, the virgin (Greek parthenos, Strong's #G3933) shall be with child and shall give birth to a son, and they shall call His name Emmanuel" (Matthew 1:22 - 23, HBFV)
The Greek word parthenos is used in eleven other places in the New Testament besides Matthew 1:23 and Luke 1:27. It is consistently translated as "virgin" or its plural and always refers to someone who is chaste physically or in two cases considered so spiritually (see 2Corinthians 11:2, Revelation 14:4). God knew what he was doing when he inspired Matthew to translate the Hebrew almah of Isaiah 7:14 into parthenos in the Greek. Its meaning in the New Testament is beyond doubt.
The First Prophecy
15. And I will put enmity between you (Satan) and the woman, and between your seed and her Seed . . . (Genesis 3:15, HBFV)
Genesis 3:15 is the first prophecy delineated in the Bible. It declares that the devil will be overcome through "her Seed," a commonly accepted reference to the Messiah. There is, however, something more to this verse. The normal process of procreation requires the seed of a MAN (sperm) to cause conception to occur. This prophecy does not mention the involvement of a male in order to produce the prophesied child because one is not needed! Christ would not be brought into the world through natural processes, but through a unique, supernatural miracle that required only a woman. The apostle Paul confirms this fact in his book to the church in Galatia (Galatians 4:4).
The Incarnation, which occurred in 5 B.C., was one of the most anticipated events in human history. Those living in Jerusalem knew the time of the promised Christ was near (Luke 2:38). Parthian Magi diligently watched for the manifestation of the King of Kings and rejoiced when they were miraculously led to Him who deserves worship (Matthew 2:1 - 2). The religious leaders at the temple also awaited the Messiah and knew he would be born in Bethlehem (verses 4 to 6). The virgin birth through Mary of the One named Immanuel (God WITH us) began the Eternal's glorious plan to redeem us from sin and offer us a way to live in love FOREVER.