donatelo
I owe you absolutely nothing as well. If I were to shoot you cold dead and take all your money, wouldn't that be immoral / injustice? You can owe someone absolutely nothing, all that means is that you don't have to provide someone with any benefit, it doesn't mean you can actively harm the other person (such as, eternal roasting in the fires of hell) just because you owe that person nothing.
With God it’s different. Not only He owes me absolutely nothing, I owe him everything including my very being and soul. So he can do with it as He pleases.
I submit to God simply because I believe this is only fair, regardless of fire/paradise. If someone gave me money and told me they'd come back later to reclaim it, I'd most certainly hand them back the money, regardless of whether I hated that person or loved them, regardless of whether they needed it or not, and regardless of whether they could punish me for not giving them back the money.
Now I believe that my life and my very being is God's... So I have no other option but to live this life in submission to its owner, regardless of the fact that He doesn't need my submission, and regardless of whether He'd punish/reward me. Should it make any difference if I knew that the person whom I owe the money, would shred it to tiny pieces once i pay them back what I owed them? No.
The other reason why I submit to God is indeed love, and lastly fear of fire, but these two, to me, are besides the point anyway. I have a duty of submitting my life to its rightful owner (worshipping God), that's the bottom line.