Following the suicide of a clinically depressed friend of mine another and I were discussing the difference between depression and faulty thinking, wrong decisions, etc. It’s an often misunderstood concept.
Clinical depression is a physical/chemical/neural brain disorder (not a personality, thinking, or spiritual disorder, although that can additionally exist). It is akin to MS, cerebral palsy, Parkinson’s, epilepsy. Talk therapy & Christian counseling help with coping skills, but are not a cure in clinical depression (or schizophrenia, clinical anxiety, OCD, bipolar, etc.).
Spiritually, we exist in this life in an imperfect body and brain due to our fallen state as a result of original sin. We die, we make wrong choices, we have “stinking thinking,” we sin, we have birth defects, cancer, heart disease, mental illness, etc. Through Christ we are made perfect (body & soul) in eternity, but in this life we live in an imperfect body and coexist in two spiritual natures within an imperfect body (and physical brain). The wonderful difference now (as Christian believers) is that we are now justified and saved from the righteous and deserved punishment for our sins through our faith in Christ’s sacrifice and God’s love for us, his children (Romans 6:23, etc,) The Apostle Paul details this in his letter to the Romans.