This is the “T” in TULIP. Total Depravity means that because of Adam’s sin, our spiritual condition is that we are dead in sin. It means that sin or depravity reaches into every aspect of our lives, there isn’t a part of my life that wasn’t affected by sin.
Key Bible passages include Genesis 2:17-18
16 And the Lord God commanded the man, “You are free to eat from any tree in the garden; 17 but you must not eat from the tree of the knowledge of good and evil, for when you eat from it you will certainly die.”
Romans 5:12
Therefore, just as sin entered the world through one man, and death through sin, and in this way death came to all people, because all sinned—”
And Ephesians 2:1-2
As for you, you were dead in your transgressions and sins, 2 in which you used to live when you followed the ways of this world and of the ruler of the kingdom of the air, the spirit who is now at work in those who are disobedient”
These verses build up the picture of how serious sin is. Sinners are not just suffering from a form of sickness, it is worse than that. If sin affects every aspect of our lives, then outside of Christ, it means that we are unable to truly do anything good, anything that pleases God. This is not saying that there aren’t things we do that are kind, good, loving, generous or even wise, noble, brave. Rathe, it is saying that our deeds are done from motives that are orientated away from God towards ourselves and towards false gods. If everything we do is first and foremost worship, then it is either done to enjoy and glorify God or to enjoy and glorify idols. Our thoughts, words and deeds are not good because they are idolatrous. This is a challenging rebuke to human pride.
Sin is serious because sin has brought death. We are utterly helpless. We cannot please God, we cannot change our lives, we cannot help ourselves or others. You don’t attempt to give medication to a corpse and you certainly don’t tell a corpse to try harder. That is how the Bible portrays us in our sin and rebellion.
That’s why salvation has to be all and only from God. He is the only one who can resuscitate us by breathing new life into us. This is why Definite Atonement, Unconditional Election and Irresistible Grace are essential and it is also why The Perseverance of the Saints becomes possible. Salvation cannot be dependent upon me in any way shape or form because I’m unable to act or even respond until the Holy Spirit gives life.