What's the Big Deal About the Virgin Birth?

Sinners beget sinners (Psalm 51:5).  Always.  

So if Joseph was the real father of Jesus,... Jesus is not spotless, not innocent, and not perfectly holy.  And as a result, we have no mediator, no imputation of Christ's righteousness (because He has no righteousness to impute to us), and no salvation.

The Good News We Almost Forgot by Kevin DeYoung

Q. What benefit do you receive from the holy conception and birth of Christ? 

He is our Mediator,  

1 Timothy 2:5,6 

• For there is one God and one Mediator between God and men, the Man Christ Jesus, 
• who gave Himself a ransom for all, to be testified in due time…. 

Hebrews 9:13-15 

• For if the blood of bulls and goats and the ashes of a heifer, sprinkling the unclean, sanctifies for the purifying of the flesh,
• how much more shall the blood of Christ, who through the eternal Spirit offered Himself without spot to God, cleanse your conscience from dead works to serve the living God? 
• And for this reason He is the Mediator of the new covenant, by means of death, for the redemption of the transgressions under the first covenant, 
• that those who are called may receive the promise of the eternal inheritance. 

and with His innocence and perfect holiness covers, in the sight of God, my sin, in which I was conceived and born.

Romans 8:3,4 

• For what the law could not do in that it was weak through the flesh, God did by sending His own Son in the likeness of sinful flesh, on account of sin: 
• He condemned sin in the flesh, 
• that the righteous requirement of the law might be fulfilled in us
• who do not walk according to the flesh but according to the Spirit. 

2 Corinthians 5:21 

• For He made Him who knew no sin to be sin for us, 
• that we might become the righteousness of God in Him. 

Galatians 4:4,5 

• But when the fullness of the time had come, God sent forth His Son, 
• born of a woman, born under the law, 
• to redeem those who were under the law, 
• that we might receive the adoption as sons. 

1 Peter 1:18,19 

• …knowing that you were not redeemed with corruptible things, like silver or gold, 
• from your aimless conduct received by tradition from your fathers,
• but with the precious blood of Christ, 
• as of a lamb without blemish and without spot.