"Grip of Grace" this book by Max Lucado is interesting. Suppose God say "Jump so high that you can touch the moon, you are saved".
Now, you can jump 3 inches high, I can jump 6 inches. Even if I can jump twice as high, it's not something I can be proud of, because both of us are still 230,000 miles away from the moon! We will never make it!
this should explain why, we can never jump(or work) our way to heaven. The distance is just too great. We truly and certainly need someone stronger(like God!) to carry us to our destination!
Christians entry to heaven is not earned by works, but by God's grace! Good works that come after that MUST NOT be us(Christians) trying to earn a seat to heaven, but of Love and Servitude to people and to God.