Resurrection of Christ, page-861

"At birth the spirit associates itself with the individual."

That suggests or sort of suggests, effectively two individuals here, of which from what I see in the Bible, this is not so.

The Bible says that upon death, the spirit returns to God, which could simply mean the spirit aspect is the breath of life.
Meaning, the body living and spirit are part and parcel of the one being, person.

Just like Gen 2:7 says, man was formed and given the breath of life and is then defined as a living soul = living being, the latter here defines what a soul means.