Belief alone without effort on our part doesn't improve our lives. When we accept something as true without acting on our conviction, we become helpless victims, waiting for change to happen, hoping God will change us miraculously. Faith is crucial to our spiritual life. But if belief were the only thing we needed to become good, we would be robots, passively waiting to be moved forward by God's power.
Trying to buy our way to heaven doesn't work either. Mindlessly saying prayers or doing good things just so God will notice and give you some credits won't change you. You can't buy goodness. It comes as a free gift from God. That's the wonder of it - God gives us a loving heart and a true perspective far beyond anything we've earned. God's love comes with our humble awareness that He is giving it to us because He loves us.
The solution is to combine good deeds and belief. Doing what is right requires activity and effort on our part. Belief requires trust and the acknowledgment that the power to do what is right comes from God.
It's a great system when you see it that way. God gets to do what only He can: give us power, desire, insight, and perspective. We get to do what only free human beings can do; choose to act the best way we can based on our understanding of what is right. This way of thinking about ourselves gives God the power that a god should have and gives us the free choice that a person should have.