Part One: Total Depravity
The best place to begin a discussion of what are called the "Doctrines of Grace" is with a discussion of total depravity. It is because man is totally depraved that grace is essential for salvation. Indeed, the evidence of man's total depravity is what led C. H. Spurgeon to preach the sermon titled "Sovereign Grace Hated by Modern Religionist." The two subjects are so entwined that the truth of one demands the other.
Two common misconceptions surround the notion of total depravity. First, total depravity does not mean absolute depravity. Man is not always as evil as he possibly could be. Man is not the epitome of Satan himself. While Satan is "intensely evil," natural man is "extensively evil." To be extensively evil means that man can do no thing perfectly.
Second, total depravity does not mean a complete absence of relative good! At this point the distinction between relative goodness and perfect, or true, goodness should be emphasized. The Heidelberg Catechism well describes this scriptural distinction in the question: What are good works? Only those which are done from true faith, according to the law of God, and to His glory. Jesus described the difference in Luke 6:33, "And if you do good to them that do good to you, what reward do you have? For even sinners do the same." The nonelect may happen to do what is according to the law of God, but not because it is the law of God, and certainly not from true faith and to His glory. They do relative good because of God's common grace and due to the remnant of the image in which they were created.
What total depravity does mean is that even though "natural" (unregenerate) man can do relative good, his actions are NEVER perfectly good from the eternal perspective, "having a form of godliness but denying its power" (II Tim. 3:5). Even the seemingly good choice of "coming" to Jesus is not good enough to save (consider Matthew 7:21-23). It is also important to remember that even though a regenerate heart is capable of doing what is truly good (a rare occurrence indeed!), it is still affected by the sinful nature. It is often that a Christian is amazed and repulsed at how selfish, hypocritical, and dreadfully evil his own heart is. This is evidenced by the words of the apostle Paul, "I know that nothing good lives in me, that is, in my sinful nature" (Rom. 7:18).
What total depravity also means is that there is an inability of natural man to do, understand, or even desire the good. The Belgic Confession is biblical when it says natural man has an "incapacity to perform what is truly good." Also, the Canons of Dort statement, "all men are. . . incapable of saving good." Jesus stated this Himself in John 15:5-6 (see also I Cor. 1:18, and 2:14). Not only does natural man not desire good, he desires evil, hates God, and is not able to desire good (Rom. 8:7).
The doctrine of total depravity humbles the human heart to its proper place of total submission to the Sovereign God upon which our salvation rests. If we arrogantly attempt to elevate our moral nature, then we inevitably begin to diminish our dependence upon God. Only those regenerated by God may truly choose Christ, and even then the Christian struggles with his depraved nature to do that which is truly good.
Reconsider Matthew 7:21 and ask yourself this question: How many of those people who walk an aisle and "choose" God, do so (1) from true faith, and (2) for His glory because God first "made them a new creation"? How many do so because of their own selfish motives for "fire insurance" or emotional discomfort created by a skilled orator? Consider your heart. Do you need to fully submit to the "author and perfector" of your salvation (Heb. 12:2)?V
Recommended reading:
Luther, Martin. The Bondage of the Will.
Packer, J.I. Evangelism and the Sovereignty of God.
Pink, A.W. The Sovereignty of God.
Spurgeon, C. H. Sermons on Sovereignty.