Love Vs. Duty

I had an interesting conversation with a muslim last Friday night while down at the 16th street mall. He explained to me that the reason he did things. I.e. Praying so many times per day with his face pointed towards the mid-east/why he practices Ramadan, etc. And he told me that he does it because he has to. Otherwise, he's not a Muslim. Then I asked him if he only did it because he had to, or if he did it because he loved Allah. And he replied that it was because he had to. This is ultimately a fundamental difference between Christians and Muslims. Christians obey God's law because they love God. Muslims do it because they have to. Also, one thing that interested me is that they are implying that they are saving themselves. When they do the so many things that they are required to do, they are basically saved. Yet, at the same time they say that God is sovereign. How does this work? They're saving themselves through their works, while at the same time saying God is sovereign?