What does the Bible says about the sinfulness of man? To what extent has sin penetrated his being? Was sin terminal?

What does the Bible say about the sinfulness of man? To what extent has sin penetrated his being? Is sin terminal which leads spiritual death or did it just made humanity sick, but able to function with spiritual insight and choices?

The Bible present man's spiritual condition as terminal and death. He is like a person who contracted a terminal disease at birth called sin. He can do nothing about it and is born dead in his sins (Eph. 2:1-10; Rom. 5:12; Col. 2:13; Gen. 6:5; Ecc. 9:3; etc.).
RC Sproul explains it as follows.

"I like to replace the term total depravity with my favorite designation, which is radical corruption. Ironically, the word radical has its roots in the Latin word for “root,” which is "radix," and it can be translated root or core. The term radical has to do with something that permeates to the core of a thing. It’s not something that is tangential or superficial, lying on the surface. The Reformed view is that the effects of the fall extend or penetrate to the core of our being. Even the English word core actually comes from the Latin word cor, which means “heart.” That is, our sin is something that comes from our hearts. In biblical terms, that means it’s from the core or very center of our existence."

Sin has rendered man spiritually dead and unable to understand or seek God (Rom. 3:10-18). It has made man unwilling and unable to hear the good news and act upon it. The sinner is not like a drowning person that gets thrown a lifeline by God that he must choose to take hold off. According to Scripture, man has drowned in his own sin and is lying dead at the bottom of the ocean (Ezekiel 37, The valley of the dry bones). He is drunk and under control of his own sin - "slaves to various passions and pleasures, passing our days in malice and envy" (Titus 3:3). Sin has penetrated his "blood" like alcohol and is now influencing all his actions. He needs a "clean-up" and resurrection first to be able to understand and act upon the good news (John 3:3, 5; Ez. 36:25-27).

Man's state of sinfulness is radical and to the core of his being. His heart is completely filled with sin. He will only desire what makes him happy. Be it evil or good things. He is an idolater at heart; worshiping his own desires for his own glory. He cannot even see from within himself his own self-righteous state. According to him, he is a relatively good person that only makes bad choices every now and then. He is not able to see himself in the light of God's goodness and holiness because he is totally cut off from God. He is like a man living in his own world where he makes the rules and sets the standards. He is auto-man on auto-pilot.

This is the crisis man is born into. The problem is he does not even realize the dire state of affairs he is born into. He will carry on with life on death-row until God steps right in front of him to bring him to a halt on his path of death. Only when he sees Jesus right before him will he realizes where to is he going and what is he busy with. Until then, life is good and he will enjoy what it offers, good and bad, to serve his evil heart of self-righteousness.

Sin has entered every fiber of man's body. His heart is the control center of his will. Without a new heart, nothing will move him to choose differently. He will only desire what is good for his own interests and to serve the sin in him. Sin is much stronger than man. According to the Bible, he is a slave to his own sin - singular (John 8:34; Rom. 6:20).

In closing, we can summarize it in the words of the Bible. "The heart is deceitful above all things, and desperately (radical) sick; who can understand it?" (Jer. 17:9). "For all of us have become like one who is unclean, And all our righteous deeds are like a filthy garment; And all of us wither like a leaf, And our iniquities, like the wind, take us away. There is no one who calls on Your name, Who arouses himself to take hold of You; For You have hidden Your face from us, And have delivered us into the power of our iniquities" (Is. 65:6-7).

What is the answer? A new heart, a new life or differently said; rebirth is needed to enable man to see Jesus, understand God, his own sin, his own crisis and the good news that can save him. Through rebirth, the dead man at the bottom of the ocean of sin will have the ability to see and understand the lifeline thrown at him. He will grab hold of it and the Father will pull Him to the surface of Christ's righteousness.