Creation
When Adam and Eve (first human beings) were initially created, they were complete, good, and without fault. They were given free will and were able to make decisions and do things which were good! They had no tendency towards committing sin. However they did have one single opportunity to sin - which would be if they ate from the tree God told them not to eat from. There were no other “do not do this” rules! And as mentioned above, since they were good, they would not sin in any area of their lives. However, the likable qualities of the tree (world), and the enemy’s misguiding influence, were external factors which could entice them to choose sin - to choose something that was not what God wanted (Genesis 3:1-7, 4:7).
Adam and Eve were tempted by the enemy and the tree, and ultimately chose to disobey God. This changed humans - it resulted in humans getting a sinful nature (tendency to do wrong). Fortunately God can change this! When someone decides to follow Jesus they become born-again/a new creation: they are restored back to the original design! There is no more sinful nature (built in desire to do wrong) which got invited in when Adam & Eve sinned.
We know this because there is no sinful nature in Heaven, and we will be taking our born-again heart, mind (soul) and spirit with us! These have already been made good and new! The only thing that we will get new after dying is a body and that is because the one we currently have is part of the earth which is going to get destroyed.
As stated previously, the things in the world and the enemy entice people to do things that are not good. If the enemy or sin is invited into a person’s life they need to acknowledge it is wrong and then repent. Then the blood of Jesus washes them clean of that sin and they are no longer internally influenced by it (2 Corinthians 5:17, Hebrews 9:13-14, 1 John 1:9, 2:15-17, John 13:10, Luke 14:33, Romans 6:18-22)!