Ro 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:
The "wherefore" relates back to Romans 3:19-23 and may be regarded as a continuation of the discussion of the universality of sin, interrupted ; Romans 3:24-5:11; by the passage on justification and its results.
have sinned
The first sin wrought the moral ruin of the race. The demonstration is simple.
(1) Death is universal (Romans 4:12,14), all die: sinless infants, moral people, religious people, equally with the depraved. For a universal effect there must be a universal cause; that cause is a state of universal sin (Romans 5:12).
(2) But this universal state must have had a cause. It did. The consequence of Adam's sin was that "the many were made sinners" (Romans 5:19)--"By the offence of one judgment came upon all men unto condemnation" (Romans 5:18).
(3) Personal sins are not meant here. From Adam to Moses death reigned (Romans 5:14), although, there being no law, personal guilt was not imputed (Romans 5:13). Accordingly, from Genesis 4:7 to Exodus 29:14 the sin-offering is not once mentioned. Then, since physical death from Adam to Moses was not due to the sinful acts of those who die (Romans 5:13), it follows that it was due to a universal sinful state, or nature, and that state is declared to be out inheritance from Adam.
(4) the moral state of fallen man is described in Scripture Genesis 6:5; 1 Kings 8:46; Psalms 14:1-3; 39:5; Jeremiah 17:9; Matthew 18:11; Mark 7:20,23; Romans 1:21; 2:1-29; 3:9-19 ; 7:24; 8:7; John 3:6; 1 Corinthians 2:14; 2 Corinthians 3:14; 4:4; Galatians 5:19-21; Ephesians 2:1-3,11,12; 4:18-22; Colossians 1:21; Hebrews 3:13; James 4:14; 1 Corinthians 15:22.
Now, we might think that this original sin didn't have an effect on humanity after Adam but the results are visible when someone dies. That is the result of Adams sin.
Today we might think it natural but this wasn't what God had in store for humanity when he made Adam and Eve.
Jesus didn't just die for our petty little sins but because it was the way to reverse this universal sin or condemnation on mankind.
We are the sum of all that is, and has been. We will be the sum of our choices.