Anyone who belongs to Christ is a new person!
To understand why Jesus was sacrificed for our sins, you have to understand what sin is. Sin is a violation of a divine law (a law that came directly from God, the Ten Commandments). Sin was brought unto the earth through man. "Therefore, just as sin entered the world through one man, and death through sin, and in this way death came to all men, because all sinned." (Romans 5:12)
God said to Adam, "Because you listened to your wife and ate from the tree about which I commanded you, ‘You must not eat of it,’ Cursed is the ground because of you; through painful toil you will eat of it all the days of your life. It will produce thorns and thistles for you, and you will eat the plants of the field. By the sweat of your brow you will eat your food until you return to the ground, since from it you were taken; for dust you are and to dust you will return." (Genesis 3: 17-19) So, the earth was cursed because of the sin that Adam and Eve committed.
Why did Jesus need to die for us?
According to the Bible, if a person sins they need a blood sacrifice to cover their sins. Jesus lived a life without sin, therefore, he was considered the perfect sacrifice to cover our sins.
The bible says: "for all have sinned and fall short of the glory of God" (Romans 3:23) and "for the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord" (Romans 6:23).
We deserve death for our sins. Because Jesus took our punishment dying on the cross, our sin debt to God was paid in full. His blood sacrifice covered our sins.
If you repent of your sins and put your full trust in Jesus Christ and His sacrifice, God will find you innocent and not guilty on the Day of Judgment.
"He has delivered us from the power of darkness and conveyed us into the kingdom of the Son of His love, in whom we have redemption through His blood, the forgiveness of sins." (Colossians 1:13-14)