God revealed to Isaiah the miraculous nature of the birth of the Messiah, the seed of Abraham. He would be born to a virgin, thus fulfilling the promise made in Eden that the Redeemer would be the seed of woman.
Isaiah 7:14, KJV
14. Therefore the Lord himself shall give you a sign; Behold, a virgin shall conceive, and bear a son, and shall call his name Immanuel.
That the prophecy recorded in Isaiah is valid is shown in the record of the Apostle Matthew and the physician Luke.
Luke 1:26-28a; 30b-35, KJV
26. And in the sixth month the angel Gabriel was sent from God unto a city of Galilee, named Nazareth,
27. To a virgin espoused to a man whose name was Joseph, of the house of David; and the virgin's name [was] Mary.
28a. And the angel came in unto her, and said, ....
30b. Fear not, Mary: for thou hast found favour with God.
31. And, behold, thou shalt conceive in thy womb, and bring forth a son, and shalt call his name JESUS.
32. He shall be great, and shall be called the Son of the Highest: and the Lord God shall give unto him the throne of his father David:
33. And he shall reign over the house of Jacob for ever; and of his kingdom there shall be no end.
34. Then said Mary unto the angel, How shall this be, seeing I know not a man?
35. And the angel answered and said unto her, The Holy Ghost shall come upon thee, and the power of the Highest shall overshadow thee: therefore also that holy thing which shall be born of thee shall be called the Son of God.
We see here that Jesus Christ as the Seed of Abraham was through the work of the Holy Spirit, conceived in the womb of the virgin Mary, a daughter of Abraham. Jesus Christ had no human father. He received His human nature from the Virgin Mary alone. This truth has, unfortunately, been corrupted into grievous error by some who claim that Mary is the mother of God. Mary is the mother of the human nature of the God-man, Jesus Christ, not the Divine nature. Martyn Lloyd-Jones, an eminent British pastor of Westminster Chapel during the 20th century, writes [God the Father, God the Son, page 262]: “As the Lord’s divine nature had no mother, so His human nature had no father.”
There are also some who wrongly teach that a completely new human nature was created for Jesus Christ [page 134f, The Modern Creation Triology, Volume 1, by Henry and John Morris]. If this were true He would not be the seed of Abraham, David, or the woman, Mary and is, therefore, directly contrary to Scripture. Martin Lloyd-Jones also clearly refutes this error by Morris and others in his book God the Father, God the Son, page 259ff.
Note that this Scripture also tells us that the work of the Holy Spirit was such that the human nature the Son took to Himself was sinless, i.e., that holy thing which shall be born of thee shall be called the Son of God. This does not say that Mary was sinless, which she was not, but only that the child was Holy or sinless. It is only because Jesus Christ was sinless that he was able to pay the penalty for our sins as well as those of His mother Mary. Scripture tells us:
1 Peter 1:18,19, NKJV
18. knowing that you were not redeemed with corruptible things, [like] silver or gold, from your aimless conduct [received] by tradition from your fathers,
19. but with the precious blood of Christ, as of a lamb without blemish and without spot.