Ezekiel 18:20 The soul who sins shall die. The son shall not bear the guilt of the father, nor the father bear the guilt of the son. The righteousness of the righteous shall be upon himself, and the wickedness of the wicked shall be upon himself.
Does this verse contradict original sin? First lets look at what original sin is. Original sin as viewed (briefly) by most Reformed/Calvinist is that we as humans are born into this world with sinful natures due to Adams sin.
A sinful nature was not man's original state at his creation:
Ecclesiastes 7:29 Truly, this only I have found: That God made man upright, But they have sought out many schemes.
Genesis 1:27 So God created man in His own image; in the image of God He created him; male and female He created them.
Adam's fall brought sin and death:
Romans 5:12 Therefore, just as through one man sin entered the world, and death through sin, and thus death spread to all men, because all sinned
And all humans are born into sin and have no righteousness:
Psalms 51:5 Behold, I was brought forth in iniquity, And in sin my mother conceived me.
Ephesians 2:3 among whom also we all once conducted ourselves in the lusts of our flesh, fulfilling the desires of the flesh and of the mind, and were by nature children of wrath, just as the others.
Ecclesiastes 9:3 This is an evil in all that is done under the sun: that one thing happens to all. Truly the hearts of the sons of men are full of evil; madness is in their hearts while they live, and after that they go to the dead.
Romans 3:10-11 As it is written: " There is none righteous, no, not one; There is none who understands; There is none who seeks after God.
Now we are condemned by our own sins. But we are not sinners because we sin, we sin because we are sinners. But if mankind's sinfulness comes from Adam what are we to think of Ezekiel 18:20? The key is in the next verse:
Ezekiel 18:21 "But if a wicked man turns from all his sins which he has committed, keeps all My statutes, and does what is lawful and right, he shall surely live; he shall not die.
God already laid out that "the soul that sins shall die". We have seen that we all sin and none are righteous, therefore we all earn this death from the start. But God in his mercy allows us to repent and live even though we don't deserve it! You see the whole 18th Chapter of Ezekiel is about repentance and if we repent we can not be held accountable for the sins of our fathers. This chapter is not discussing the fact of the Fall of Adam and it's consequence on mankind, but it is showing repentance and how we don't deserve it!