If you don't understand about original sin, I don't think you've understood anything about God, the Bible, or human history even. Adam was created perfect, and Eve out of Adam. Eve was deceived by Satan into thinking that they could be like God. (Satan is still using this deception today, in pretty much every man-made religion, that is, everything but Christ.) Adam and Eve disobeyed God, their Creator, being warned previously that such disobedience would cause them to die. Die they did, and the human race was cursed with death and all of creation cursed with them. Paradise was lost--mankind was expelled from the garden of Eden. Death, violence, sickness entered the world. Human history has been shaped and plagued by these things.
How could God, the ultimate righteous Judge, let lawbreakers be forgiven of their crimes? Adam and every person born since (except Jesus) have broken the law the Creator put down for our protection. In order to teach men that they are sinners and not like God, God gave men the Law of Moses. It was meant to teach men they could never on their own reach the perfection needed to have fellowship with God. If men put their trust in God -- had faith in Him -- they would be saved. From the time of Moses to Christ, this meant doing what God said to do: follow the law. So the Israelites, God's chosen people, tried and failed to follow God's law, sacrificed unblemished animals to cover over their sins for a time when they failed to follow the law.
The problem with sacrificing animals is it only covered over their sins, it did not pay the penalty for sin which was death. God sent what was needed to fix the situation - a perfect sacrifice to pay the penalty for all sins for all time. God sent His Son to be born as a man, live as we do, be tempted in all things as we are, but live a perfect, sinless life. His Son, Jesus, willingly was tortured and killed to pay the penalty for our sins. He died in our place. But as Adam brought death to the whole human race, the last Adam: Jesus brought the hope of life back to the whole race.
separation from God fellowship with God
ruled by Satan ruled by Christ
death eternal life
So if you don't understand about original sin, you don't understand why death and disease and suffering effects the world so much, you don't understand why Christ had to come to the world, or why he had to suffer and die, and why Christ's resurrection is our only hope.
1 Corinthians 15
15 Now I’m making known to you, brothers, the gospel that I proclaimed to you, which you accepted, on which you have taken your stand, 2 and by which you are also being saved if you hold firmly to the message I proclaimed to you—unless, of course, your faith was worthless.
3 For I passed on to you the most important points that I received: The Messiah died for our sins according to the Scriptures, 4 he was buried, he was raised on the third day according to the Scriptures—and is still alive!— 5 and he was seen by Cephas, and then by the Twelve. 6 After that, he was seen by more than 500 brothers at one time, most of whom are still alive, though some have died. 7 Next he was seen by James, then by all the apostles, 8 and finally he was seen by me, as though I were born abnormally late.
9 For I am the least of the apostles and not even fit to be called an apostle because I persecuted God’s church. 10 But by God’s grace I am what I am, and his grace shown to me was not wasted. Instead, I worked harder than all the others—not I, of course, but God’s grace that was with me. 11 So, whether it was I or the others, this is what we preach, and this is what you believed.
The Resurrection of the Dead
12 Now if we preach that the Messiah has been raised from the dead, how can some of you keep claiming there is no resurrection of the dead? 13 If there is no resurrection of the dead, then the Messiah has not been raised, 14 and if the Messiah has not been raised, then our message means nothing and your faith means nothing. 15 In addition, we are found to be false witnesses about God because we testified on God’s behalf that he raised the Messiah—whom he did not raise if in fact it is true that the dead are not raised. 16 For if the dead are not raised, then the Messiah has not been raised, 17 and if the Messiah has not been raised, your faith is worthless and you are still imprisoned by your sins. 18 Yes, even those who have died believing in the Messiah are lost. 19 If we have set our hopes on the Messiah in this life only, we deserve more pity than any other people.
20 But at this moment the Messiah stands risen from the dead, the first one offered in the harvest of those who have died. 21 For since death came through a man, the resurrection of the dead also came through a man. 22 For as in Adam all die, so also in the Messiah will all be made alive. 23 However, this will happen to each person in the proper order: first the Messiah, then those who belong to the Messiah when he comes. 24 Then the end will come, when after he has done away with every ruler and every authority and power, the Messiah hands over the kingdom to God the Father. 25 For he must rule until God puts all the Messiah’s enemies under his feet. 26 The last enemy to be done away with is death, 27 for “God has put everything under his feet.” Now when he says, “Everything has been put under him,” this clearly excludes the one who put everything under him. 28 But when everything has been put under him, then the Son himself will also become subject to the one who put everything under him, so that God may be all in all.