Why do you say that all we have to do to have eternal life is to believe in Jesus? That sounds far too simple to me. Surely God expects us to live good lives before He'll let us into heaven, doesn't He?
You have asked a very important question, and I pray you will consider it seriously, because nothing–absolutely nothing–is more important than our eternal salvation. Our time on earth lasts only a few decades, but eternity is forever.
If God simply took all our good deeds and bad deeds and balanced them against each other, then eventually some people might be good enough to go to heaven. Many people think this must be the way God operates–but it isn’t, and it’s very important to understand why.
You see, the real question is this: How good do you have to be to get into heaven? The answer may shock you: You have to be perfect. Why? Because God is perfect, and even one sin will keep you away from His holy presence. The Bible says of God, “Your eyes are too pure to look on evil; you cannot tolerate wrong” (Habakkuk 1:13). This is why we can’t save ourselves by our own good works, for we can never–never–be good enough.
This is why we need Christ. He came into the world for one reason: To save us from our sins. He was without sin, but all of our sins were laid on Him, and He died in our place. Don’t trust yourself any longer, but by faith trust Christ, “For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life” (John 3:16).