What is the explanation for Yajur Veda 19.37?
We need to read and understand the underlying sloka/verse to decipher the correct meaning intended in the Vedas. But you need to be careful with western translations when relying on their interpretations of vedas. I will write the sanskrit verse below and provide meaning for it, and then clarify what its intention is thereafter.
But first, one thing I need to caveat - you said "I mean how it is possible, because once you are dead your soul goes for reincarnation. And takes birth on earth. So the souls of the grandfather and great grandfather will also go for reincarnation/rebirth. " -- that is not what the samhita portion of any veda says. That theory (you can never prove punarjanma in reality, it is just a theory) first came into picture in the vedAnta portion texts. As you are asking a question on samhita portion, lets stick to samhita knowledge base in understanding meaning of this verse. You cannot apply a non-samhita theory when trying to understand that samhita verse, right? Apples to oranges otherwise, so please stand corrected on that end.
Now, your verse is from the Vajasaneyi shaka texts of Shukla Yajur Veda. That kanda is for the Soutramani Yagnya and the set of verses 1 through 21, within which is the 19th verse you quoted, are meant for purification of the sacrificer and oblations to fathers essentially. So you need to keep that context in mind. Now your particular verse is the actual verse -
punántu mā pitáraḥ somyā́saḥ punántu mā pitāmahā́ḥ || punántu prápitāmahāḥ pavítreṇa śatā́yuṣā || punántu mā pitāmahā́ḥ somyā́saḥ punántu prápitāmahāḥ || pavítreṇa śatā́yuṣā víśvam ā́yur vy àśnavai |
Meaning: 'punAna' word underlying above verse means - wash off or destroy or purify. I am sure you know what 'pitarah' and 'pitamah' and 'prapitamah' means. The verse is literally asking our ancestors to purify us & allow us to live our full life. That is the meaning of it.
If you know Hindi, you can also see the correct meaning being provided below:
As you can see, 'cleanse' is the wrong word used. It is 'purify'. Secondly 'sieve of a century' is an incorrect translation, heck I do not see that word 'sieve' at all in that sloka. So, we need to be careful when relying on western translations of our Vedas.
So, you can see that this verse has nothing to do with asking someone to 'clean' us. It is worshipping our pitru devAs seeking their blessings to purify us & our life. That is all that is meant by it. Purification means removal of our sins, for there is no other way to purify us.
Hope this answers your question.
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