"Total depravity" sounds like an unwelcome and antiquated teaching that reminds people of really BAD people and awful human history, like the Holocaust. This first of what are called the "five points of Calvinism" has anchored the remainder of the truths of this system. Without a right and deep understanding of this teaching, there is no real need for unconditional election, the certainly of atonement through the death of Christ, the need for sovereign, Holy Spirit given and irresistible grace and the surety of final perseverance to the end of life. Many people discount the sinfulness of anyone. It is not fashionable, even in conservative, Christian, Bible-believing circles to talk about the extent and depth of human sinfulness. People want to believe they are a bit "defective" but not really damned and doomed sinners without hope, and without heaven as a final end. We always want to believe "the best" about ourselves and therefore hate John Newton's line in the song, Amazing Grace, "that saved a wretch like me." But, that is what we are biblically.
The Scriptural basis for the doctrine of total depravity is vast and pervasive. The remarkable statement of God Himself to Noah and the few saved through the flood is astounding -- "Never again will I curse the ground because of man, even though every inclination of his heart is evil from childhood" (Genesis 8:21). Spiritual death is the result of the fall of mankind through Adam and Eve (Genesis 2:16, 17; Romans 5:12). Ephesians 2:1-3 tells us that conversion to Christ gives us life from the dead -- "As for you, you were dead in your transgressions and sins . . ." (cf. Colossians 2:13) Psalm 51:5 tells us this condition is from conception -- "Surely I was sinful at birth, sinful from the time my mother conceived me." Ecclesiastes 9:3 tells us "the hearts of men, moreover, are full of evil and there is madness in their hearts while they live . . ." and Jeremiah 17:9 proclaims, "The heart is deceitful above all things and beyond cure. Who can understand it?" The death knell is given in Romans 3:23, "for all have sinned and fall short of the glory of God." Many other verses can be cited, but the evidence is irrefutable--humankind without a savior is intensively and extensively in rebellion against God, since that is the essential meaning of "sin." It's not a mistaken condition caused by our circumstances, not an unfortunate set of bad parents or siblings, not a misstep caused by Satan or some other enemy of our soul. It is our settled condition as sons and daughters of Adam and Eve.
What This DOESN'T Mean
Total depravity does NOT mean humankind is as bad as it can be. It does not mean that people cannot do, in theirs and others viewpoints, kind and respectable acts. It does NOT mean that people will always act out their "worst sides." But, consistent with this teaching is the doctrine of "common grace." The rain that falls, for instance, falls on the "righteous and unrighteous" (Matthew 5:45). The sun that shines, the food we eat and so on and so forth comes from a perfect and loving heavenly Father without discrimination of a person's faith stance. These are still "gifts" but "common" to all and thus instances of "common grace."
What this DOES Mean
The teaching of total depravity, properly understood and accepted, drives one to realize he or she cannot "earn" or "merit" of "deserve" God's kindness and His salvation. We are intrinsically sinful. We are not sinful merely because we sin. The death-knell to a "merit-based" or "works-based" approach to being right with God rests right here. Everyone who is right with God through faith in Jesus Christ got there purely and exclusively by God's unmerited favor and kindness. If "saved," we are still sinners saved by grace, always to be aware of Bunyan's precious saying, "There, but for the grace of God, go I!" Any other way of looking at gaining God's favor is humanly devised and humanly based.
Depravity Includes Total Inability
The genius of the Reformers was to understand that this depravity is truly TOTAL. Every thought, action, word, deed, desire, motivation and inward longing, apart from an external spiritual renovation, has been permeated, not merely affected, by this sinful nature and reality. We CANNOT choose good over evil by ourselves. Like the leopard which cannot change its spots, the sinful man or woman cannot change his or her nature (Jeremiah 13:23). Jesus Himself said that a "bad tree cannot bear good fruit" (Matthew 7:16-18; 12:33). He said, "no one can come to me unless the Father who sent me draws him . . ." (John 6:44, 65). The ability and power to see and do good in God's sight is a gift from God (1 Corinthians 4:7).
The immediate and rather violent, at times, rejection of this aspect of depravity or the extent of human sinfulness is that man has a will that is free. What that means is that this will remains "unaffected" by the depravity that permeates our beings. Clearly, this cannot be the case. There is not a separate "compartment" in our being where a "neutral" will resides waiting to choose between good and evil. We will default to evil, if left to ourselves and our choices without divine intervention. Humankind's will is in bondage to depravity by nature and by choice.
To get around this obvious problem of inability, some theologies have posited a "prevenient" kind of grace that God has given to every person as a result of the saving atonement of Christ.(cf. Wesleyanism) "Christ died for everyone" means, therefore, that God has given to everyone in the world that has or will ever exist enough of undeserved favor that the will is made able to choose right from wrong and eternal good from evil. Such a position cannot be directly proven from the Bible. It has to be "inferred" from a theory that lack of human freedom means and is equivalent to lack of human responsibility. But, responsibility does not need freedom to be valid.
Is humankind then merely "robots" set on a world stage with God as the Grand Puppeteer? Does man actually have a "choice?" Proponents of total depravity decidedly say, "of course." We can freely choose that which is in accord with our nature! God will not "force" us to choose evil, for that would make Him the author of evil. WE freely and responsibly choose what we want. It is the "want" that is the problem. We do NOT naturally want what God wants.
The only HOPE is divine intervention outside of our natures and outside of our possibilities. That brings us to the second point of the Synod of Dort's declaration -- "unconditional election."