The Biblical Fact of Total Depravity:
How do you view natural man? As good? How do you view yourself in your sin? Are you mostly good, but do some bad things? The Bible's testimony of the moral/spiritual quality of man is clear: man, in his sin, in his fallen nature, and even the fleshly-remaining part of the Christian, is morally depraved.
The Old Testament Witness:
The doctrine of Total Depravity is certainly an Old Testament reality.
Genesis 6:5 The LORD saw that the wickedness of man was great in the earth, and that every intention of the thoughts of his heart was only evil continually.
But there are many more texts. Go look up: Job 14:4, Psalm 14:1-4, Psalm 51, Ecclesiastes 9:3, Jeremiah 17:9
But what about the New Testament? Realize, we don’t believe there are different gods in the Old Testament in comparison to the New. We believe the same Triune God worked in both. And therefore, we should find a consistency of doctrine from Old Testament to New Testament.
The New Testament Witness:
Romans 3:10-18 as it is written: "None is righteous, no, not one; (11) no one understands; no one seeks for God. (12) All have turned aside; together they have become worthless; no one does good, not even one." (13) "Their throat is an open grave; they use their tongues to deceive." "The venom of asps is under their lips." (14) "Their mouth is full of curses and bitterness." (15) "Their feet are swift to shed blood; (16) in their paths are ruin and misery, (17) and the way of peace they have not known." (18) "There is no fear of God before their eyes."
Notice the New Testament text of Romans 3 is literally quoting Old Testament texts. Together they testify inerrantly that man is guilty of sin, a sinner, sins, is liable for God’s eternal wrath in hell, and to the miseries of this life. But there are numerous other texts that make the same point. Even Jesus will teaches us that nothing good comes out of the heart of men. Go read: Matthew 15:16-20, Mark 7:18-23, Romans 1:28-32, Ephesians 2:1-3, and Galatians 5:19-21.
The Clarification of the Doctrine:
But, by "Total Depravity" we do not mean that man is as bad as he could be. Satan, we could argue, is the most evil being. But every person is not Satan. Adolph Hitler, we could argue, is one of the most evil persons to ever have existed. Every person is not Hitler though. That's not what we mean. The "total" of "total depravity" does not modify "depravity." We are not saying "all people are as bad as they could be." Rather the "total" of "total depravity" references all the aspects of the internal thought world of man. In this sense, "total" means "comprehensive." We are saying that man is comprehensively depraved.
For instance, you parents, why do you not have to teach a child to disobey? Why do they know how to disobey naturally? Who taught them, if they are indeed morally neutral or good? They don’t need teaching! If you’re a parent, you know what I mean. How come your pre-one-year-old seems to get angry at you for feeding them, putting them to bed, getting them up, WRONG!? But manners, politeness, or cleaning their rooms - why is that an act of divine power when it happens!? Or, why are your motives for obedience also tainted with self-love? It is because man's will is in subjection to his corrupt nature.
But the doctrine of Total Depravity is entirely practical. It destroys any argument for the validity of pride or arrogance. When you lose a child, when you lose a job, when you serve the Lord and bad things happen, it’s easy - and immoral - to tell yourself, “God, you’re wrong for taking this away from me. If I were God, I would have given it to myself.” Who are you, O man! Is it not right and appropriate, that, when we go through real, dark, and deep travail of soul, over sin, over pain, over loss, that we first recognize THAT I AM NOT OWED ANY GOOD THING FROM GOD. In your sinfulness, you are first owed his wrath, and the miseries of this life. But if you thought you were owed something from God, you’d be prideful and thankless when you have something good. But considering that you are owed God’s wrath, and the miseries of this life, then the children we do have, an imperfect job that provides for my family, and a humble place to serve in the kingdom, are things we can be thankful for. And when loss of a child, firing, or self-forgetting service in the kingdom comes - while the pain and loss is real, and deep - you don’t have to get mad at God, you don’t have to doubt his love, because your sin renders you worthy of the worst miseries in this life. And while some miseries are genuinely hard, and dark - they are not THE WORST. But God knows the loss you suffer, because he sent his Son to die on the cross for your sin - in a more brutal death than any of us will ever experience. He knows. You’re not forgotten. But that doesn’t mean we may lie to ourselves about how worthy or good we are.
Man's rebellion against God is the moral quality of his entire internal thought world. By "depraved" we mean man is not only "not righteous before God", he doesn't want to be righteous, and he cannot be righteous; he doesn't like God, and he does want to be like God. He wants to be God in every area of his life. But he’d prefer to kill God. Righteousness according to God and the Bible is disgusting to natural man. Man is morally and spiritually warped. He is a rebel before God.
Think of it this way: every other religion thinks man is basically good. But such a position is a demonstration of man's moral depravity. We will call evil "good" in every other religion in order to escape the reality of having been judged by the thrice-holy God. And there is no part of man that isn't controlled by his rebellion. There is no part that is morally good, or acceptable to God. You are dead to God, in your trespasses and sin:
Ephesians 2:1-3 And you were dead in the trespasses and sins (2) in which you once walked, following the course of this world, following the prince of the power of the air, the spirit that is now at work in the sons of disobedience— (3) among whom we all once lived in the passions of our flesh, carrying out the desires of the body and the mind, and were by nature children of wrath, like the rest of mankind.