Sin nature, soul, salvation, repentance

To answer your first question: God gave Adam and Eve a choice to serve God willingly or to reject Him. In Genesis 2:17 God made it clear that Adam and Eve were not to eat the fruit of the tree or they would surely die. Because of Adam and Eve’s rebellion against God, this caused Adam’s sin nature and death to be passed down through all generations since.

The answer to your second question is yes, the soul is immortal and Hell is real (Psalm 22:26; 23:6; Ecclesiastes 12:7; Daniel 12:2-3; Matthew 25:46 and 1 Corinthians 15:12-19). Daniel 12:2 tells us that “And many of them who sleep in the dust of the earth shall awake, some to everlasting life, and some to shame and everlasting contempt”.

You also asked why we repent if Christ saves us. 1st John 1:9 says ” If we confess our sins, He is faithful and just to forgive us our sins, and cleanse us from all unrighteousness”. Though believers are forgiven at the point of salvation, there is also an ongoing sense in which believers need to confess sin and experience forgiveness and cleansing. Cleansing was an important part of the Mosaic Law, mentioned some 14 times in the book of Leviticus alone. It was the goal of those who brought a sacrifice to the Lord in the tabernacle and temple.

When we have an argument with others, it creates a barrier to fellowship. Since a barrier between us and God will always be our fault, our need for confession is important for our relationship to God. You should not wait to repent. 2 Corinthians 6:2 says (For he saith. I have heard thee in a time accepted, and in the day of salvation I have succored thee: behold, now is the accepted time, behold, now is the day of salvation). Repentance is making a complete change toward God. That is not earning salvation. That is changing your mind about your eternal destination. You cannot be saved if you do not repent. The only time it is too late to be forgiven of your sins is when you reach the point of death (Hebrews 9:27).

You asked if it was possible to sell your soul. There is nothing in the Bible that implies a person can sell their soul. There is nothing in the Bible that even implies that it is possible to bargain with the Devil.