Once upon a time, a rich man asked Jesus, how he could attain eternal life. The man had lived a good life. Jesus told him to sell all his property, give the money to the poor, and then follow Jesus. The man became sad, because it was too much to ask for.
Jesus’ disciples were confused: “How can anyone be saved?”
Jesus answered: “To the man it is impossible, but to God it isn’t. To God everything is possible.”

This is the answer of Christianity.

We are bound by our own selfishness. We love ourselves more than anyone else. Even our efforts to obtain salvation is selfishness as well. Do we have any hope?

The answer Christianity gives differs from the answers of all the other religions. The focus is not on us and what we have to do. Jesus Christ is the center of everything. He did, what none of us could not. He took upon Himself our transgressions and atoned our sins when he died on the Cross.

That is why there exists a perfect forgiveness in God’s heart. It is proclaimed to us in the Bible. It is called "gospel", "The good news". We own this God's promise through faith. Through faith in Christ we are saved and get to heaven. When I have been baptized in the name of the Father, and the Son, and the Holy Spirit, I know I belong to God. On the Day of Judgment, when I stand before God, I don't even try to answer for my sins, because Jesus has already received the full punishment for all the sins of my life.

You can be sure about getting to heaven, because you can be sure about Jesus and his work.

For by grace you have been saved through faith. And this is not your own doing; it is the gift of God, not a result of works, so that no one may boast.
(Ephesians 2:8-9, ESV)