Even people who don’t believe in God are guided by moral intuitions and obligations. But they lack a rational basis for them. We all understand that good and evil aren’t just what we “feel” as an individual, and that there’s a moral standard above us. This standard can’t come from other people, or else, morality would be dictated by society or powerful individuals (and there’d be no grounds for condemning, for example, the Holocaust). The standard also can’t come from natural evolutionary processes, because moral law deals with more than mere survival.
People who don’t believe in God, still insist morality is justified. But without God, believing that compassion, kindness, and honesty are valuable isn’t warranted. Because those qualities exist it’s more intellectually consistent to say that there is a divine Law-Giver; who is the source of our moral intuitions.