Who are you? What carries your karma? What is rebirth?
In Vedas, Agni unites the generations, and moves from one generation to another. This Agni knows of what is manifest, we call him jātavedas. As he who is born of tanu, (or reflexively, himself) he is called the tanūnapāt. From the father to the son, from parents to children, from the mother’s womb to the child, from the Guru to the śiṣya – Agni alone is the thread. We do the yajña in Agni because then, it is a symbol that Agni shall carry our good karma and refine it. We pray for offspring to the Devas so that whatever merit we have incurred is transferred to the immortal part of us lingering in this world. Just go through some of the various verses of the sages of Vedas:-
“nitye toke dīdivāṃsam s-ve dame”
“O Agni, you shine in your eternal abode, in the offspring”
“jātena jātam ati sa pra sarsṛte yaṃ yaṃ yujyaṃ kṛṇute brahmaṇaspatiḥ”
“By what is born, he extends himself over what is born – whoever makes union with Brahmaṇaspati”
“pra jāyemahi rudra, prajābhiḥ”
“Let us be manifest, O Rudra, through the offspring”
“prajābhir agne amṛtatvam āśyām”
“O Agni, might I attain immortality through offspring”
“tanūṣu viśvā bhuvanā ni yemire prasārayanta purudha prajā anu”
“All beings are set down within their tanus, yet they have extended themselves variously through offspring”
svāṃ prajāṃ pitaraṃ pitryaṃ saha āvareṣu adadhus tantum ātatam
“The ancestors have placed their ancestral power in their own later offspring, as a thread stretched”
In the case of rebirth of a “person”, there has to be attributes of that person which need to be born again. Based on karma. Already this happens when you produce your children. And that makes “you” immortal. Therefore the Taittirīya Brāhmaṇa says,
prajām anu pra jāyase, tad u te martyāmṛtam
“You are born again in your offspring, that o Mortal, is immortality for you”.
This is why we do our worship to our ancestors in Brahmanism, and perform śrāddha rituals for the dead. Because what they chose to do, how they chose to live forms an important part of our person, which is then moulded by the environment around us. Through honouring them, we are respecting the “us” in ourselves.
You aren’t literally a dog reincarnated or your person going to be born as some werewolf in your next birth. All this stems from the unnatural fantasy of some dissociation disorder which the Upanishadic era kings experienced, vexed with the megalomaniac growth of urban culture and the illusion of individuality. (Something we are also going to face in the near future) The nature is a whole, and it acts that way. Each of our actions impact here, this world. How you choose to program yourself and your children impacts how your lineage will behave, what characteristics they will have. How efficient the society and the rulers implement the Ṛta affects how the society as a whole will progress.
All this is the reality of this universe.
This is also why the Guru in Indian tradition is revered on the same plane as one’s father. In the era of gurukula, the Guru literally “formed” the person of the student, surpassed what the student naturally was made, of himself. Therefore, through upanayana, one takes a second birth – one is ready to refine his instincts, his person and his deeds.
Why do you feel you are suffering for your “past life” sins which you as a person cannot know (unless you do some confabulation)? What you suffer from depends upon what you choose to do, what your person instinctively would choose to do, how the society has moulded you. Beyond this, anything that happens due to nature’s calamities are not stoppable and it is your duty to bear them, because you didn’t “choose” to breathe, “choose” to be born, and “choose” to live.
I will speak later on the problem of the “illusion of choice and absolute free-will”, which the society of our times is going to suffer from.
why the Guru in Indian tradition is revered on the same plane as one’s father?
This is in fact, very much explained in even the older kalpa literature. For example, Āpastamba says, on the glorification of the Guru who leads the person to light :-
sa hi vidyātastaṃ janayati
tat śreṣṭhaṃ janma
śarīram eva mātāpitarau janayataḥ
“It is he (ācārya) who gives birth to the student.
That birth is the best
Just the śarīra is produced by the parents”.
How Guru acts as representative of Agni :-
bhaikṣaṃ haviṣā saṃstutaṃ tatra ācāryo devatā arthe,
āhavanīya arthe ca
“Alms obtained (by begging, by a brahmacārī) is praised as the havis (oblation)
intended for the Ācārya, who is the devatā and the Āhavanīya Agni”.
Even the verse I quoted from Brāhmaṇam is quoted by all dharmasūtras while discussing immortality and offspring :-
atha-apy asya prajātim amṛtam āmnāya āha | prajām anu prajāyase tad u te martyāmṛtam iti
atha api sa eva-ayaṃ virūḍhaḥ pṛthak pratyakṣeṇa-upalabhyate dṛśyate ca api sārūpyaṃ dehatvam eva anyat
Even then, the śruti has stated that one’s offspring is immortality – as in “You are born in your offspring, that for you mortal, is immortality”. (verse from Taittirīya brāhmaṇa) This one would even perceive clearly as dehatva and likeliness in appearance is reflected in offspring.
Later, these works were all interpolated to conform with the four āśramas and karma-rebirth theories. This is why we cannot bring forth a single verse from Vedas in support of the presently existent dogma of rebirth or karma, but we find this is plenty in Upaniṣads and later works.