"For what profit is it to a man if he gains the whole world, and loses his own soul?" (Matthew 16:26)
To me, that sentence just doesn't make any sense. I was raised in a religious family, and the definition for the soul was something in you, the lives on after you die. If that were so, "loses his own soul" would be a silly thing to say, at best. It would infer that God will strike successful business people down, or something strange like that.
But that could not have been what the Bible said. That was what it was translated to say.
The word soul did not exist in Biblical times.
The word soul, originated in 970 AD from the word sawol, centuries after Mathew was written.
If the Bible's translation had said:
"For what profit is it to a man if he gains the whole world, and loses his own life?"
like it should have, it would make sense, even to a small child.
The word "soul", in the sense we use it today, did not exist in Hebrew or Aramaic,
It existed in Greek. Ancient Greeks typically referred to the soul as psyche (as in modern English psychology). Aristotle's works in Latin translation, used the word anima (as in animated), which also means "breath". In the New Testament, the original Greek word used is "Psyche" which in Ancient and Modern Greek means soul.

Plato, drawing on the words of his teacher Socrates, considered the soul as the essence of a person. He considered this essence as an incorporeal, eternal occupant of our being, the determines how we behave. As bodies die the soul is continually reborn in subsequent bodies. The Platonic soul had three parts:
1. the logos (mind, nous, ego, or reason)
2. the thymos (emotion, superego, or spiritedness)
3. the pathos (appetitive, id, or carnal)

The logos was the charioteer, directing the horses balance of appetite and spirit. It allows for logic to prevail, and for the optimisation of balance.
The thymos comprises our emotional motive, that which drives us to acts of bravery and glory. If left unchecked, it leads to hubris -- the most fatal of all flaws in the Greek view.
The pathos equates to the appetite that drives humankind to seek out its basic bodily needs. When the passion controls us, it drives us to hedonism in all forms. In the Ancient Greek view, this is the basal and most feral state.