Adam

Romans 5
19 For as by one man's disobedience many were made sinners, so by the obedience of one shall many be made righteous.

In Romans 4, we were sent back to the Old Testament, to read about Abraham. In this chapter, we are again sent back to Genesis, but this time to remember the story of Adam.

Genesis 2
17 But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die.

These two passages provide the lesson on our sinful essence. And, of the saving grace of Jesus Christ.

If there is a list of ten or fifteen Bible passages most important to the Christian faith, my guess is this passage from Genesis 2 is on it.