Our First Parents 4

Romans 1
18 For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who hold the truth in unrighteousness;
19 because that which may be known of God is manifest in them; for God hath showed it unto them.

A little bit of God is manifest in us, is part of our being. And by this, we therefore know righteousness and unrighteousness.

More From Romans 5
12 Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:

And, where does our sin nature come from? Our first parents, no doubt. But, does it really matter where our sin came from? It is innate, and we spend our days, inventing un-righteousness. Like Adam, we cannot resist the apple.
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