Here is a quote from Athanasius I wanted to read on Monday night, but never got to it. (Athanasius was an early church leader
in Alexandria (in Egypt) in the 300s. He is famous for standing against false teaching in his day, specifically false teaching that
denied the Trinity and the full deity of Christ. (You can check him out on Wikipedia and Theopedia (recommended!) and see his writings on the CCLE here.))
This quote gives an excellent analogy to explain why the event of the Son of God taking a body affects the entire human race. Enjoy:
For naturally, since the Word of God was above all, when He offered His own temple and bodily instrument as a substitute for the life of all, He fulfilled in death all that was required. Naturally also, through this union of the immortal Son of God with our human nature, all men were clothed with incorruption in the promise of the resurrection. For the solidarity of mankind is such that, by virtue of the Word’s indwelling in a single human body, the corruption which goes with death has lost its power over all. You know how it is when some great king enters a large city and dwells in one of its houses; because of his dwelling in that single house, the whole city is honored, and enemies and robbers cease to molest it. Even so is it with the King of all; He has come into our country and dwelt in one body amidst the many, and in consequence the designs of the enemy against mankind have been foiled and the corruption of death, which formerly held them in its power, has simply ceased to be. For the human race would have perished utterly had not the Lord and Savior of all, the Son of God, come among us to put an end to death.
From On the Incarnation of the Word