What determines the destiny and future fate of the living entities?

Answer

This creation is governed by the three modes of material nature. The living entities have fallen into the whirlpool of the three modes and have become helpless, thus they perform fruitful deeds and some purifying rituals and believe they are happy. This is why their activities are called ‘the drama of māyā.’ When such people die their destination is decided by the Lord through the time factor called destiny, as per their performed deeds. The results from their ritualistic ceremonies are flickering and thus they, when elevated to heavenly planets, cannot stay there for a long period of time. As stated in the Bhagavad Gītā, ābrahma bhivanāl lokāḥ punar āvartinaḥ, “All the planetary systems in this material world up to the highest planet, Brahmaloka, are filled with the misery of repeated birth and death.” The Lord created this universe so people can experience the fruitful results of their actions, which is why the living entity sometimes goes downward taking birth in the lower species; as well as sometimes becoming elevated and taking a higher birth, all depending on the quality and quantity of their performed karma. The Supreme Lord decides the living entities next destination.

As stated in the Nyāya Śāstra, phalam ata upapatteḥ, “The future destination of a person depends on the results of their present deeds.” The Vedānta Sūtra also states, upapatteś ca, “The scriptures demonstrate and prove that destiny decides the future fate of a living entity according to their present actions.” Just as a living entity obtains different destinations per the categorical results of their fruitful work along with the pious rituals they have performed, similarly a devotee realizes the Lord per the quality and sincerity of their devotional service to Him. Just as the light from a lamp is one color, if that light is seen through a crystal or prism it is divided into many colors; and just as sound is one thing, when it is heard through a drum, a saxophone, or a flute it sounds different. Similarly although the process of worship is one, according to the realizations of a particular devotee the result of their worship differs, which is why worship rewards different destinations depending on the quality of worship of the performer.

Source

Śrīmad Bhāgavatam, 11.24.15, Volume 15, Page 107