PrincessofGod18, Dave's answer is good, and mine is longer.
Think of the places in the Bible where it talks about the final judgement of people. We have a high priest who has been tempted in every way as we could be, yet He was without sin. When Jesus died, He wasn't just electrocuted, sliced up, beheaded. He was indeed betrayed, scorned, blasphemed and disdained, ripped up in suffering, publicly humiliated in nakedness, and even endured a period of either being or feeling forsaken by God - all while being sinless. He took on every awful thing that could be done to humanity. In that final judgement, we don't have someone who can't feel for what humans experience but we have Jesus. He will judge righteously.
This makes sense because He was there all the time, walking in the garden with the first people, shutting the door of the Ark, talking with Abraham and destroying the wicked and irreparable societies of pagan nations, giving the Law to Moses, establishing a system to shine the light of His goodness (if we would just walk in His ways instead of our increasing wickedness when we walk our own ways).
The understanding that sin resulted in death was understood from the beginning as evidenced when Abel brought a lamb sacrifice and Cain's sacrifice of produce wasn't respected. God gave Cain advice but Cain rejected it and grew more evil. Noah offered animal sacrifices when he came out of the ark, having been prepared in advance to carry extra of the appropriate animals. The sacrificial system was noted when Moses was speaking with Pharoah and was established in the Law after they left Egypt. The reminder year by year was important then, as it played out the same story that we would see more clearly looking back on this side of the earthly life of Jesus.
Sin is that awful that it demanded a sacrifice - and now we have that sacrifice once for all. Sin is not an arbitrary situation, a list of things that God put on man not to do. Sin hurts people and societies. Evil, which is what stands behind habitual sin and rebellion against God's holy and righteous nature and ways, will finally be done away with, but for now it exists because God created us with choice and doesn't take that away. We can choose to do His ways (which are good) or we can choose to do evil. We can choose to repent of evil, but what evil we did do still requires that payment, and we needed to see that.
God isn't interested in throwing people into condemnation but wants all people to be saved and come to the knowledge of the Truth. Sin is that awful that the truth is it required the death of His Son and the power of His resurrection. Sin is that awful that we are reminded that there is no further sacrifice if we ignore the once for all sacrifice of Jesus - He won't be dying again for our sins.
Along those lines, just believing a set of words is not enough. God shows His great love for us in that while we were yet sinners, God did this for us. This message is powerful and will work its way into the very hearts of those who really believe. God obviously seeks a people who recognize His goodness and want to clean up and conform their thinking to His righteous ways. Keep working through questions like these and you'll find yourself understanding more of the depth of the love of God shown us in Christ.
