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Jesus had to atone for the specific penalties laid upon mankind for original sin. We see these penalties in Genesis chapter 3. We find the answer to the virgin birth in the penalty placed upon Eve. The penalty for Eve is in Genesis 3 verse 16:
Unto the woman he said, I will greatly multiply thy sorrow and thy conception; in sorrow thou shalt bring forth children; and thy desire shall be to thy husband, and he shall rule over thee.
In order to pay the full penalties of sin, Jesus had to come into the world through the pain of childbirth, because the pain of childbirth was God’s penalty for the sin of Eve.
What of the second part of Eve's penalty? "and thy desire shall be to thy husband, and he shall rule over thee."
Genesis 2: 21-24
“And the LORD God caused a deep sleep to fall upon Adam, and he slept: and he took one of his ribs, and closed up the flesh instead thereof; 22 And the rib, which the LORD God had taken from man, made he a woman, and brought her unto the man. 23 And Adam said, This is now bone of my bones, and flesh of my flesh: she shall be called Woman, because she was taken out of Man. 24 Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh”.
God could have made Eve from dust, as he did Adam, but, He did not. If He had, then Eve would be a totally separate creature with no direct connection to man. Woman was meant to be a companion for man, and, man a companion for woman, two with opposite attributes that perfectly completed each other.
They were to be of one flesh, equal counterparts. Because Eve was fooled by satan and lead the man to sin, therefore, she would be lead, by the man, as punishment for that sin.
Because of Eve’s sin, she was punished by being placed subject to the man, which is a cause of struggle and strife between man and woman to this very day. We see the effects of original sin, and, the downward spiral thereof, so deeply woven into society.
We were meant to be equal, each with our own equal functions and abilities that, when placed together, made mankind complete. Sin corrupted this.
Mary was a virgin, and unmarried, when Jesus was conceived by the power of the Holy Spirit. Although Joseph took her as his wife prior to Jesus birth, she remained a virgin until after Jesus was born. Mary knew no man, and had no husband, so, she was not subject to the desire and rule of a husband.
Furthermore; historically, the actual marriage of a Jewish man and woman would take place upon the “yihud”, or “unification”, which is the consummation of the marriage.
Through the virgin birth of an “unmarried” woman, Jesus would conquer the penalties placed on Eve.
I'd like to add that Jesus also paid the price of the penalties placed upon Adam.
"Cursed is the ground because of you; In toil you will eat of it, All the days of your life. 18“Both thorns and thistles it shall grow for you; And you will eat the plants of the field; 19 By the sweat of your face You will eat bread, till you return to the ground, Because from it you were taken; For you are dust, And to dust you shall return.”
God punished Adam for his sin by removing him from paradise. Adam would now have to toil for survival, and, Adam would eventually die and return to the ground from which he came. Jesus worked for His food, lodgings and clothes, just like any man, so, He toiled as a carpenter. The crown of thorns placed on His head represents the payment for the sin of Adam. Because Jesus died with no sin, He would conquer death. He would not go into the ground and His body would not decay, thus freeing us from going back to the dust from which we came.
Jesus also paid the spiritual penalty of sin; eternal condemnation and separation from God, when He became sin on the cross. When Jesus cried out "My God, why have you forsaken me?", and, "I thirst", Jesus had become sin. As sin, He became separated from God. Knowing this, Jesus declares: "It is accomplished."
Thank you, Jesus.