People believe in all sorts of different religions and Gods. I would rather use the word faith. Religions are a set of rules, faith is what you believe in.
I believe in Karma. Not as a supreme being, but as a way of life. To me, Karma is the idea that, in some direct or indirect way, the actions I take today come with reflecting consequences that will show themselves at some stage in the future. The more consistent the action, the more the consequence will reflect it.
For me, that's all the more reason to do good today.
Be a good person. Give. Contribute. Commit to something worthwhile, something with a greater purpose, something you're passionate about. Give it your all. Your actions and efforts will be rewarded.