Why do we mix faith in God with moral values?

I am discovering Islam and reading the Quran. I am also looking through this website to add some perspectives. Something that I don't understand is why Islam mixes faith in God - let's say "personal" relationship between you and God - and moral values applied to behaviour among men and women. I get giving rules to help people know right from wrong, but most people just follow rules without actually thinking about them, because that's just the way it should be. Not questioning rules is never a good thing. These rules, especially the most restrictive ones, create frustration and hypocrisy among men and women. How can someone be considered to have good moral values if inside he or she is filled with envy, anger, or shame? On the other hand, how can someone with strong moral and ethical values while living freely from those rules be considered a bad person? For me this second choice seems much healthier and faithful in regards to God's expectations than the first one. So I am quite confused... If I am a good person and God knows it, why should I follow rules that will make me feel bad and ultimately become someone not worthy of God's expectations?