Shvetashvataropaniśhad "(श्वेताश्वतरोपनिषद) says that if someone thinks that just by following the path of karma, doing good actions but without surrendering to God, in other words, if someone thinks they can attain God without bhakti, just by doing good actions, Vedas says a word, “pramurhah” (which means a great fool).
That person is a great fool, because they will go to swarg (celestial abode) on the basis of their good actions, but then they'll get returned here. They only stay for a limited period of time in swarg, then they're bound to come back in this world and take birth again. Maybe even in the lower species, before they get a chance to be born as human again.
So, if someone thinks the path of karma is going to take them to their ultimate goal, they're mistaken. And that's why he said, “Adhyatmanta eva isha.” All those other paths are taking you somewhere, but they keep you within the realm of maya. They don't take you beyond maya.
