If I were put in charge of determining right and wrong, morality would be very simple, and very easy. Each person would be afforded certain rights: life, property, truth, fidelity in contract, perhaps a few others. All rules would derive from this central principle: Do not violate another person's rights. From this rule, our basic moral prohibitions would arise: do not murder, do not steal, do not break promises, be faithful to one's spouse, do not lie (under most circumstances). Beyond these prohibitions, my ethical system would have no requirements. It would effectively render humans moral by default. After all, it takes a great deal of effort to carry out a major theft, to tell compelling lies, to carry on an affair, to commit a murder, and we do not usually regard any of these things as components of a happy life. Perhaps you too find my moral system tempting.
The moral codes of both the Old and New Testaments contain a fair number of prohibitions, including those that I have included in my system. For me, one of the great difficulties of faith is that Christian morality asks full commitment of oneself to others - "Love the Lord your God with all your heart and with all your soul and with all your strength" and "Love your neighbor as yourself". Adhering to the prohibitions described above is the smallest part of carrying out these commands.
These demands are brutal. By following them, we lose time, money, dreams, passions, blood. I think that many people reject the faith because of them. And so they reject a world where these commands will be the law of the land and of the heart.