"Gospel" means "good news"
Think of what Adam and Eve lost: perfect life for themselves and their children's children. Had they not sinned, they would still be here and we would never get sick, never die.
Their act of disobedience has caused much pain; but it did not change God's purpose for mankind. Genesis 3:15 tells of a time when Satan's rule will end and Jesus will direct the affairs of God's kingdom.
So, our commission is to proclaim the "good news" and bring comfort to those who have been kicked about by the travails of this world.