Look closely though:
Jerimiah 1: 4-5 The word of the LORD came to me, saying:
“Before I formed you in the womb I knew you, and before you were born I set you apart and appointed you as a prophet to the nations.”
Yes, that's a very good hint (as pointed out in post 2), and notice, God didn't say "when I formed you in the womb", He said "
before I formed you in the womb"!
Our individual spirit which is our most essential self
must exist on some level
before our mother or father conceives our physical body. (before conception)
We read that directly: before he was even conceived, already God knew Jeremiah! Not when he was formed, but before.
And confirmed in another way for example in this verse:
Ecclesiastes 12:7 before the dust returns to the ground from which it came and the spirit returns to God who gave it.
since the body is dust:
Genesis 3:19 By the sweat of your brow you will eat your bread, until you return to the ground--because out of it were you taken. For dust you are, and to dust you shall return."
So, body (flesh) and spirit of a person are not the same thing, and the body will return to dust, and the spirit to God who
"gave it".
So, God, already knowing Jeremiah's spirit before even conception also already knew/knows all individual's spirits, before they have any physical body, before they are formed in the womb, for each individual person.
(Also, we can consider the a common mainstream interpretation that a soul is what happens when a spirit (from God) resides in a physical body)
At death of the physical body, the body returns to dust, as scripture says, but that is not who we are. We are spirit in essence (and that's the only ultimate lasting part of us). Christ said:
John 6:63 The Spirit gives life; the flesh profits nothing. The words I have spoken to you are spirit and they are life.
So, the only question that happens then is when does God place a spirit into a physical body, during pregnancy?
Only a portion often said to be a fraction like 1/2 of fertilized human eggs/embryos are actually viable on average == the ones which are healthy and are going to naturally survive and implant and thrive.
The others naturally die, just as God intended. The natural abortion of un-viable embryos (or for other reasons like a physical problem in the ovary or such).
So....
Would God put a spirit/soul into a fertilized egg that He can see is not viable and will be naturally aborted (as He designed to happen)?
It seems to better fit what we know of God -- Just, Fair, Merciful -- that He would choose to put a human soul into a growing human embryo that is viable/functional, and
able to naturally grow. And that He would
not put a human soul into an embryo that He can see is flawed or damaged/unviable, and He can see will naturally die in just days or soon.
Then consider that also, the soul is often associated with various levels of human consciousness, including for example even levels that are functioning during sleep in the form of dream consciousness, and even more subtle levels, or the 'subconsciousness'.
Those are brain states -- functions of the human brain. So, it's reasonable to think the human soul is temporarily housed in the human brain. That would imply that the earliest a human soul would be in a physical body is after the brain is sufficiently developed to have some level of consciousness.
So, it seems the general feeling most people have that there is a huge shift when the developing baby
begins to have an ability to move, kick and
respond to music and such -- that feeling corresponds to an deeply profound
change.