"We certainly believe that it is through the grace of the Lord Jesus Christ that we are saved…"
– Acts 15:11 (ISV)
"By his grace they are justified freely through the redemption that is in Christ Jesus, whom God offered as a place where atonement by Christ's blood could occur through faith. He did this to demonstrate his righteousness, because he had waited patiently to deal with sins committed in the past." – Romans 3:24-25
A lot of people believe that because God is good, He will overlook their sins when they die. "Hey, He will understand, I had it bad; He is full of love, so He’ll let me into heaven." Let me tell you that the exact thing that they believe will get them into heaven, that is God's goodness, is the thing that will keep them out.
Let us look at a natural example. Let's say that you are standing before a judge and you are accused of rape, murder, drug trafficking and all sorts of bad stuff. There is ample evidence that clearly prove that you are guilty. Imagine you say to the judge, "Look, I know you are a good man. Can't you show me mercy and overlook my crimes?" You know what? The judge will look at you and say, "Because I am a good man I must make sure that you are punished. If I am not just, I can not be good."
God is just. He will not go against His Word. He said sinners will be punished and that settles it. But for Christians there is hope. One day when you stand before God, He will not say, "There is ample evidence to throw you in hell, but I will not because I know you believe that Jesus died for you." I rather believe He will say, "Welcome my child! I find NO evidence of sin in you!" That is what it means to be justified (Acts 13:38-39, Rom 5:21) "Just-As-If-I’d never sinned". If you never sinned, there would be no evidence, right? But we have sinned, and it is our belief in Jesus' death on the cross for our sins that wipes the evidence away.
Grace is something you can not earn by doing good deeds (Rom 11:6), but you do good because you are thankful (Rom 6:15-18). Imagine you messed up badly by going 80mph in a 15mph zone, right in front of a school where there were plenty of signs warning you. You were involved in a high speed chase, and the cops caught you eventually. You were given a $25,000 fine, or 5 years imprisonment. Your dad arrived at the police station and said he would pay the fine so that you can be free. How would your attitude be towards your dad? You will have a thankful heart and will probably do what he expects of you. The same thing goes for the grace of God.
Jesus carried all your sin because he loves you.