As long as the techniques for helping warriors to endure distress were used for the warrior purposes, the great metaphysical error was undeveloped. This was perhaps the high point in ancient Indo-European Civilization, that is, when the Inward Soul was reached primarily for the purpose of helping warriors to victory. When attaining the Soul Within became an end in itself decline set in. The priest class became ascendant over the warrior class. The Soul Within was declared the Kingdom of God Within, and the primary purpose of existence was now to attain this God or Soul Within. Material life, including the warrior life, was degraded and the Great Spiritual Blockade of material life and material evolution began in earnest.
All the Revealed Religions followed this Inward Path in what has since been called the Perennial Philosophy. Perhaps some branches sought to return the balance between warriors and priests. Perhaps Zarathushtra, or his ancestors, diverged from the main group for this reason. But all branches continued the great error of defining the Soul Within as God, and all branches continued the Great Spiritual Blockade against the material world.
Theological materialism seeks to address this ancient error. Tirips (formerly the Spirit which could be called the Spark of the Soul) is defined as the inward material force activating material life to evolve toward Godhood.
I do not reject the Soul Within as the secularists do, I affirm the Soul Within as the Involutionary Inward Path perhaps first discovered by ancient Proto-Indo-Europeans and later continued in the revealed religions. I define Godhood as that which we must materially evolve to, activated by Tirips Within, which is the Evolutionary Outward Path to Godhood.
We could describe that period when the Soul Within was declared God as a great ancient metaphysical error which over time led to general decline.