This is similar to another question. Brahma Sutras 3.2.38-3.2.41 (here listed as Chapter III, Section II, Adhikarana VIII - https://www.wisdomlib.org/hinduism/book/brahma-sutras/d/doc74952.html) says:
Adhikarana summary: Iswara the giver of the fruits of actions
Brahma-Sutra 3.2.38: Sanskrit text and English translation.
फलमतः, उपपत्तेः ॥ ३८ ॥
In Rig Veda I.164.20 and in 3.1.1 of Mundaka Upanishad (page 51), there was a mention about 2 birds perching on a branch of a tree.
दवा सुपर्णा सयुजा सखाया समानं वर्क्षं परि षस्वजाते | तयोरन्यः पिप्पलं
सवाद्वत्त्यनश्नन्नन्यो अभि चाकशीति ||
Two Birds with fair wings, knit with bonds of friendship, in the same sheltering tree have found a refuge. One ...
Rig veda III.20.3 says
अग्ने भूरीणि तव जातवेदो देव सवधावो.अम्र्तस्य नाम | याश्च माया मायिनां
विश्वमिन्व तवे पूर्वीः सन्दधुःप्र्ष्टबन्धो ||
Agni was praised as jataveda - knower of births
So it was mentioned in Rig veda itself about rebirth.
Be it the people with materialistic outlook or fence sitters from religious world, their perception of Karma, ...
So what is even the necessity for starting such a karmic loop?
According to the Brahma Sutras, karma is beginningless; the Jivas who are trapped in samsara have always been in it.
Ramanujacharya has stated in his commentary on the Brahma Sutras:
Although the individual souls and their deeds form an eternal stream, without a beginning, yet non-...