On experiences of a physical or spiritual nature

On experiences of a physical or spiritual nature:
“...Anything we experience as being in us, and which we see can also exist in wholly inanimate bodies, must be attributed only to our body. On the other hand, anything in us which we cannot conceive in any way as capable of belonging to a body must be attributed to our soul. Thus, because we have no conception of the body as thinking in any way at all, we have reason to believe that every kind of thought present in us belongs to the soul. And since we do not doubt that there are inanimate bodies which can move in as many different ways as our bodies, if not more, and which have as much heat or more […], we must believe that all the heat and all the movements present in us, in so far as they do not depend on thought, belong solely to the body” (AT XI:329, CSM I:329).

Regarding the necessity of the recognition that the physical body and the phenomena/noumena that is the mind co-exists with the spiritual essence (the soul):
"We need to recognize that the soul is really joined to the whole body, and that we cannot properly say that it exists in any one part of the body to the exclusion of the others. For the body is a unity which is in a sense indivisible because of the arrangement of its organs, these being so related to one another that the removal of any one of them renders the whole body defective. And the soul is of such a nature that it has no relation to extension, or to the dimensions or other properties of the matter of which the body is composed: it is related solely to the whole assemblage of the body's organs. This is obvious from our inability to conceive of a half or a third of a soul, or of the extension which a soul occupies. Nor does the soul become any smaller if we cut off some part of the body, but it becomes completely separate from the body when we break up the assemblage of the body's organs” (AT XI:351, CSM I:339)

Despite the immateriality of the soul, because the mind creates it, it exists.

Descartes' error here is that by the time he wrote The Passions of the Soul, Europe had rediscovered much of the Latin and Greek philosophers' theories regarding the soul.

As well, priestly kingdoms run by Jews influenced by the Essene may have been conquered by Roman armies so as to ensure Pax Romana.

Indeed, a Greek philosopher named Plato first wrote of the soul, and it was incorporated in Christian ideology due to the Greco-Roman influence on Jewish thought , first with Alexander the Great's conquest of Asia Minor and the Middle East, and later with the establishment of Pax Romana, the schism into West and East Roman Empires with Rome and Constantinople circa 325 CE.

Thus, by the time the Dark Ages fell over Europe circa 500 CE, the widespread chaos due to plagues and bands both of marauding invaders and local hooligans, the dynamics of civilization and religion almost came to a standstill.

Yet the pagan idea of the soul was later incorporated after Peter's later mission to introduce the Christ to Gentiles (non-Jews) due to the violent martyrdom (death by stoning) suffered by early Christians by Jews.

So, the soul of which Descartes speaks was inculcated from birth by the Catholic Church, after 500 years of earnest monks illuminating the Bible...