God exists?

I sat on the pews of my church where families and friends have gathered to honor the love and peace we have been given by God. We have been taught to love and to forgive. We have the power to do good for others and our purpose is to serve God. I have always believed this to be true. God gives me a reason to live, He brings peace into my heart and soul, He forgives me no matter what I do, and He holds me when I question my existence.

But then there's this arguement:

"I'm tired of hearing about God all the time. What has He got to do with anything? Does he pay tuition? People just don't understand. It's all a matter of ideas, and God is just one idea I don't accept. It's not important. I am not going out and be immoral or commit crimes because I don't believe in God. I don't even think about it. It's just that I get tired of Him getting credit for all the things the human race achieves through its own stubborn effort. There simply is no blasted God!"

I respect all beliefs whether it disagrees with mine or not. But this arguement has got me thinking, "Why do we need to serve Him? He brought us life, but I just don't understand why it's all about Him all of a sudden. I've learned the meaning of life through His heart and eyes, but I don't understand why He has taken the credit for every thing man kind has done. If anyone knows, please inform me. I do believe in Him and I do love Him, but someone just clarify this for me.