Why does Protestantism believe in the unbiblical idea of an immortal soul going either to heaven or hell when their founder thought otherwise?

Answer 1

Because Protestantism did not really break away from the Catholic religion due to 'beliefs'. They mainly broke away from the 'authority'; and kept the same beliefs in-tact.

Answer:

The "immortal soul" doctrine began in the Garden of Eden:

"...the serpent said unto the woman, Ye shall not surely die." (Gen.3:4)

It was adopted by the succeeding generations of rebellious man, his world-ruling empires and his religions... all "believing" it to be true, accepting it as unproved fact [and rejecting the Truth of God's Word -- "...the soul that sinneth, it shall die." - Ezek.18:4 & 20 ].

"...thou shalt surely die." (Gen.2:17)

Beginning with the first world empire this side of the flood, Babylon, with its "mystery religion," from which most of today's social and religious customs and traditions stem... the "immortal soul" doctrine thrived [thrives].

Finally, the Greek philosophers wrote it down in their "books of wisdom" and taught it in their academies. And the doctrines of the "immortality of the soul' and other convoluted philosophical teachings were institutionalized by them [and are still taught in today's academies and universities]... and the next world-ruling empire that succeeded them -- Rome -- adopted it and adapted to it; which the deceived world inherited, again, in both its societies and religions.

The Catholic church merely inherited the "immortal soul" doctrine from the Roman Empire... who ultimately inherited it from Babylon... who inherited it from across the flood, where their ancient ancestors first "believed" what they were told by the serpent, and obeyed his voice.

"Protestantism" isn't the result of the beliefs of "one founder." Different people at different times and places separated themselves from the catholic church for this or that reason. That's why we have so many different names of "Protestant denominations" today... like Lutherans, Calvinists, Baptists, as well as more than 400 others.

"Protestantism" didn't reject all of Catholicism's beliefs when each one branched off and separated from their "mother." And for the vast majority of them... the doctrine of "the immortality of the soul" was never rejected or a cause of separation.

God's Word has simply never been believed by most people [even religious people]. And still isn't, today.

The serpent's ancient lie is still thriving in the world... believed and cherished by people and cultures everywhere [even alleged "atheist" Chinese "pray" to their "immortal" dead ancestors]. "Protestantism" never gave the "immortal soul" doctrine much thought at all as a reason for "protest," as each one in their own time parted from their "mother." Satan gave it to man from the beginning... man rejected the Truth of God's Word ["...thou shalt surely die..."], and most people "believe" what they're told without proof.

Another Answer:

Because not only the Bible clearly teaches it, it is something that is self-evident to any spiritually conscious individual.

Daniel 12:2 - "And many of them that sleep in the dust of the earth shall awake, some to everlasting life, and some to shame and everlasting contempt." Mark 9:44 - "Where their worm dieth not, and the fire is not quenched."

Even from the scientific point of view, we know from the theory of relativity that time is physical property that is affected by mass, velocity and other variables, those physical properties do not apply to our consciousness, which is essentially information, or software not hardware and is not subject to physical laws.