If we think of our mind as the engine through which the totality of our thoughts are produced, the source from which our willful contemplation springs, we understand this is a mysterious, marvelous thing. (Ps 139:14)
In the physical, our mind is evidently our brain, the organ or vessel through which our soul expresses and reveals itself in thoughts, ideas, and imaginations: an incredibly complex, biological machine comprising chemicals and electricity through which the metaphysical and physical interact; it’s how our souls engage the universe, at least for now.
It follows then that a mind may be sound and healthy (2Ti 1:7), or it may be corrupt (1Ti 6:5), reprobate (Ro 1:28), broken and twisted such that it cannot rightly fulfill its purpose.
A mind may also be inconsistent, holding contrary beliefs and opinions, we might say double-minded, resulting in a pattern of instability and unpredictability (Jas 1:8), or a mind might be defiled (Tit 1:15), dirty and polluted with things that ought not to be within it. A mind might also be weak, feeble (1Th 5:14), untrained and incapable of strenuous activity, or simply blind (2Co 4:4), unable to rightly perceive reality at all.
In particular, our mind might be carnal, at enmity with God (Ro 8:7a), as opposed to a spiritual mind, rightly engaging and integrating metaphysical reality with the physical. (Ro 8:6) The difference between a carnal and a spiritual mind is exposed by attitudes or beliefs with respect to Torah, God’s Law: the carnal mind always resists some aspect of Torah; it cannot submit to the whole of Torah (Ro 8:7) — rather, it relentlessly insists on having its own way, in some way. This is the only means whereby we may reliably distinguish the carnal mind from the spiritual. (He 4:12)
Each time we willfully choose a path contrary to God’s definition of moral reality in Torah, we literally corrupt the physiological, neurological circuits of our own brains; we build in patterns of pathology into the very wiring of our own nervous systems, making it more and more difficult for us to reason and think clearly.* (Pr 5:22)
As with any notion of health, mental pathology is a matter of degree. So, no matter what state we find ourselves in, there’s something we can do to move to a better place — and we should. (Is 55:7)
God calls us to be renewed in the spirit of our minds (Ep 4:23-24), transformed by a continuous retraining of our thought patterns so that we might prove God’s will (Ro 12:2), such that we might have the mind of Christ (Php 2:5), to have His thought patterns flowing freely and regularly through ours. This happens as we hide God’s laws in our hearts, meditate on them, and take heed to our ways to ensure that every thought pattern aligns with Torah. (Ps 119:9-11) As we abide in Him like this we actually do have His mind at work within. (1Co 2:16)
* See first comment below