In Bhagavad-gita (4.11) it is said, ye yatha mam prapadyante tams tathaiva bhajamy aham: the Supreme Personality of Godhead is the supreme judge who rewards or punishes different persons according to their surrender unto His lotus feet. Therefore it can actually be seen that although karmis and bhaktas may work in the same place, at the same time, with the same energy and with the same ambition, they achieve different results. The karmis transmigrate through different bodies in the cycle of birth and death, sometimes going upward and sometimes downward, thus suffering the results of their actions in the karma-cakra, the cycle of birth and death. The devotees, however, because of fully surrendering at the lotus feet of the Lord, are never baffled in their attempts. Although externally they work almost like the karmis, the devotees go back home, back to Godhead, and achieve success in every effort. The demons or atheists have faith in their own endeavors, but although they work very hard day and night, they cannot get any more than their destiny. The devotees, however, can surpass the reactions of karma and achieve wonderful results, even without effort. It is also said, phalena pariciyate: one’s success or defeat in any activity is understood by its result. There are many karmis in the dress of devotees, but the Supreme Personality of Godhead can detect their purpose. The karmis want to use the property of the Lord for their selfish sense gratification, but a devotee endeavors to use the Lord’s property for God’s service. Therefore a devotee is always distinct from the karmis, although the karmis may dress like devotees. As confirmed in Bhagavad-gita (3.9), yajnarthat karmano ‘nyatra loko ‘yam karma-bandhanah. One who works for Lord Vishnu is free from this material world, and after giving up his body he goes back home, back to Godhead. A karmi, however, although externally working like a devotee, is entangled in his nondevotional activity, and thus he suffers the tribulations of material existence. Thus from the results achieved by the karmis and devotees, one can understand the presence of the Supreme Personality of Godhead, who acts differently for the karmis and jnanis than for the devotees. The author of Sri Caitanyacaritamrta therefore says:
Krishna-bhakta—-niskama, ataeva ‘santa’
The karmis who desire sense gratification, the jnanis who aspire for the liberation of merging into the existence of the Supreme, and the yogis who seek material success in mystic power are all restless, and ultimately they are baffled. But the devotee, who does not expect any personal benefit and whose only ambition is to spread the glories of the Supreme Personality of Godhead, is blessed with all the auspicious results of bhakti-yoga, without hard labor.
Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Eighth Canto, Chapter 9 – Text 28