Bhagavad-Gita: Chapter 9, Verse 21

Rudra Vaisnava Sampradaya:

Visnuswami

Sridhara Swami's Commentary

Those jivas or living entities reach Swargaloka the heavenly regions due to following the rituals prescribed in the Vedas of karma kanda or actions for rewards. After having enjoyed celestial delights extensively in the form of exquisite pleasure both physical and subtle for a long duration when their stock of merits becomes is finished they again descend to the world of mortals subject to samsara the perpetual cycle of birth and death. With the samsara from the previous birth fresh upon them they take birth in a family of performers of Vedic rituals where desirous of enjoying the delights of heaven they begin the procedure all over again and thus they come and go, back and forth lifetime after lifetime unceasingly.

Brahma Vaisnava Sampradaya:

Madhvacarya

Madhvacarya's Commentary

This verse clarifies in no uncertain terms that pandering to the demigods and canvassing of lesser gods have serious defects and limitations. Whereas worship and propitiation of the Supreme Lord Krishna is superior and the results are eternal.

Sri Vaisnava Sampradaya:

Ramanuja

Ramanuja's Commentary

The compound word trai-vidya denotes the lower spiritual sciences known as karma kanda or actions for fruitive rewards also enjoined in the three Vedas. Persons who perform worship for rewards are known as trai-vidya and are not devotees of the Supreme Lord as they have desires other than devotion to Lord Krishna or His authorised avatars or incarnations and expansions and so they revolve perpetually in samsara the endless cycle of birth and death. The devotees of Lord Krishna who understand Him as the goal to be known and the highest attainment are indeed the mahatmanas or great beings and as stated in verse 14 they inspiringly sing His glories and as stated in verse 15 they enthusiastically learn and enlighten each other about all aspects of His divine glory intensely focusing on Him exclusively in remembrance and meditation as their sole ambition in life and the acme of their ambition. To the contrary those votaries who are addicted to studying the three Vedas for fruitive rewards are known as trai- vidya and they desire Svargaloka the heavenly planets where there is no old age and disease and everyone may partake of Soma or the heavenly nectar after offering it to the demigods and lesser divinities, such votaries enjoy in full energy and bliss as prescribed in the Rig Veda, Sama Veda and Yajus Veda where the Atharva Veda was extracted. The ordinary sins which obstruct the passage of a jiva or embodied being from this world to Svargaloka are thus dissolved by the worship and adoration of Indra the heavenly chief and entering the heavenly spheres they reap their rewards of exquisite heavenly delights never realising that it is the Supreme Lord Krishna alone who sanctions those rewards and that Indra is merely His representative. Thus those of fruitive desires abandon themselves to the full pursuit of delectable pleasures fully accessible in the vast regions of Svargaloka. But after a long duration of time, once their accumulated merit has been exhausted and the time allotment for their heavenly sojourn has expired they again fall back into material existence of samsara.

Thus those who hanker after material delights following the karma kanda sections of the Vedas, ignoring the superior spiritual knowledge found in the Vedas as well revolve up and down, back and forth obtaining lives of elevations and recessions. The word gatim denoting destination comes from the words gat - agatam meaning transitory states with no permanence this infers that the enjoyments of Swargaloka are of a trivial and temporary nature involving a revocation and termination. Whereas the mahatmanas hanker only for the Supreme Lord, giving themselves completely in bhakti or ardent loving devotion to Him and thus they assuredly achieve the eternal spiritual worlds never returning and attain the Supreme Lord Krishna who is immeasurable, inexpressible and inconceivable annada or bliss personified. Additional characteristics distinguishing the mahatmanas is given next.

Kumara Vaisnava Sampradaya:

Nimbaditya

Kesava Kasmiri's Commentary

What happens after one has fully enjoyed heavenly delights exhausting all their merit? They must take birth again in the worlds of mortals and begin accumulating sufficient merit all over again by performing the same rituals prescribed in the Vedas for entering the celestial spheres to enjoy heavenly delights all due to motivation of desires. Again and again they must be imprisoned inside a mothers womb for nine months, lifetime after lifetime revolving in this cycle unceasingly because they hanker so much for heavenly pleasures. But when their merit is used up again they are in transition down to the cycle of birth and death and then back to heaven incessantly repeating the same process over and over.