In Ethics: Discovering Right and Wrong, Louis Pojman notes six reasons why belief in God motivates moral behavior:^[1]

1. If there is a God, then good will win out over evil. If I knew that good was going to win over evil, then I would want to be on the side of good by acting morally.
2. If God exists, then cosmic justice reigns in the universe. If God does not exist, I have to ask myself the question, why be good if I can get away with being bad when it seems to be to my advantage? If God does exist, however, I am motivated to be good because I may one day be judged by God and rewarded or punished for my moral choices.
3. If Theism is true, moral reasons always override nonmoral reasons. Sometimes, it seems that acting immorally would produce a greater good — maybe a man could abandon his family to become a doctor and save hundreds of lives. Without God, there is no reason to say that he should stay with his family. But, with God, we can say that his duty to his family overrides his duty to others. Consequently, if God exists, it is always right to do what is right and to choose to do right over what might seem most beneficial. Without God, we cannot justifiably say this.
4. If theism is true, then there is a God who loves and cares for us—his love inspires us. If God exists, then He is a loving heavenly Father, and His love fills us with gratitude and motivates us to make greater sacrifices than we might otherwise make because we want to please our Creator.
5. If there is a God who created us in His image, all persons are of equal worth. Without God, Pojman notes that we are left to conclude as did Nietzsche that some humans, namely those who are stronger, are of greater worth than those who are weaker. But this insults our common understanding of the equal intrinsic value of all humans. With God, all humans are of equal value because they are all God’s image-bearers.
6. If God exists, we have a compelling solution to the posterity problem. The posterity problem asks, why should we make sacrifices now in consideration of the needs of future generations (think protecting the environment, for example)? Without God, it might be considered morally justifiable only to consider the needs of the living. But, with God, we have reason to do good to future generations whom God loves and who also bear His image.

Belief in God makes the world a more moral place and, thus, a better place. So, let’s make the world a better place by believing in God ourselves and by making the case for faith in God!

^[1] Pojman, Louis P., and James Fieser. Ethics: Discovering Right and Wrong. Cengage Learning, 2017, Chapter 12, Section 12-3a.