1362
Śrīmad-Bhāgavatam
[Canto 3, Ch. 31]
a child is born, it is to be understood that his particular type of body is the beginning of another set of activities, and when an old man dies, it is to be understood that one set of reactionary activity is finished.
We can see that, because of different reactionary activities, one man is born in a rich family, and another is born in a poor family, although both of them are born in the same place, in the same moment and the same atmosphere. One who is carrying pious activity with him is given a chance to take his birth in a rich or pious family, and one who is carrying impious activity is given a chance to take birth in a lower, poor family. The change of body means a change to a different field of activities. Similarly, when the body of the boy changes into that of a youth, the boyish activities change into youthful activities.
It is clear that a particular body is given to the living entity for a particular type of activity. This process is going on perpetually, from a time which is impossible to trace out. Vaiṣṇava poets say, therefore,  anādi karama-phale , which means that these actions and reactions of one's activity cannot be traced, for they may even continue from the last millennium of Brahmā's birth to the next millennium. We have seen the example in the life of Nārada Muni. In one millennium he was the son of a maidservant, and in the next millennium he became a great sage.
TEXTS 45-46
द्रव्योपलब्धिस्थानस्य द्रव्येक्षायोग्यता यदा ।
तत्पञ्चत्वमहंमानादुत्पत्तिर्द्रव्यदर्शनम् ॥४५॥
यथाक्षणोर्द्रव्यावयवदर्शनायोग्यता यदा ।
तदेव चक्षुषो द्रष्टुर्द्रष्टुत्वायोग्यतानयोः ॥४६॥
dravyopalabdhi-sthānasya
dravyekṣāyogyatā yadā
tat pañcatvam aham mānād
utpattir dravya-darśanam
yathākṣṇor dravyāvayava-
darśanāyogyatā yadā
tadaiva cakṣuṣo draṣṭur
draṣṭṭvāyogyatānayoḥ