But Scripture is clear about the extent of our depravity: “The whole head is sick and the whole heart is faint. From the sole of the foot even to the head there is nothing sound in it” (Isa. 1:5–6).  The word total in the expression “total depravity” refers to the fact that sin has so thoroughly infected us that no part of our being—mind, affections, or will—is free from the taint of sin. We’re totally dead spiritually.  Like an array of corpses ranging from freshly dead to thoroughly decomposed, some may be in a more advanced state of putrefaction than others, but all are equally dead. Our inability is total, too, because there is absolutely nothing we can do to earn our salvation.  If we are to be awakened from that death and redeemed from our sin, God must do it, and God alone. MacArthur, J. (2009). The Sinner Neither Willing nor Able. In Proclaiming a cross-centered theology (p. 93). Wheaton, IL: Crossway.

Sin is a disease which pervades and runs through every part of our moral constitution and every faculty of our minds. The understanding, the affections, the reasoning powers, the will, are all more or less infected. Even the conscience is so blinded that it cannot be depended on as a sure guide, and is as likely to lead men wrong as right, unless it is enlightened by the Holy Ghost. In short, “from the sole of the foot even unto the head there is no soundness” about us. (Isa. 1:6.)  The disease may be veiled under a thin covering of courtesy, politeness, good manners, and outward decorum; but it lies deep down in the constitution. Ryle, J. C. (1889). Holiness: Its Nature, Hindrances, Difficulties and Roots (p. 5). London: William Hunt and Company.