Overview

Total Depravity is the foundational concept in the debate between Calvinism and Non-Calvinism, and understanding it is crucial for understanding the points of contention.

If when Calvinists said Total Depravity - they just meant that:

Mankind is completely separated from God because of sin and there is nothing any man could will, work, or do to earn salvation and redemption.

If this was the case, then all of Christendom should affirm it; however, that is not the true meaning of the T in the Calvinist TULIP systematic. 

Often, when Calvinist defend the idea of Total Depravity, they start with a definition like the above that many Christians would initially agree with—one that emphasizes humanity's separation from God due to sin and our inability to earn salvation. However, this definition conveniently glosses over the main point of contention of implying that mankind's depravity also makes us incapable of responding freely to all the calls of Christ to turn to him, repent, and believe. According to the Calvinist, these calls by Christ are powerless on their own and no depraved human can respond positively to the Gospel call of their own free will, even if that message is brought by the Holy Spirit.

To better illustrate the Calvinist perspective, some have started using the term "Total Inability." This nuance highlights the point of the definition that causes disagreement. Calvinists believe humanity is not only spiritually depraved but also entirely unable to accept the Gospel on their own unless God first supernaturally regenerates their hearts. Calvinists argue that because we cannot save ourselves from sin, we also cannot, by our own will, turn to Christ for Him to save us—because that would imply we "saved ourselves" or produced a "good work." To non-calvinists this would be like saying I healed myself of sickness because I brought myself to a hospital. 

The natural end point from the Calvinist definition of depravity is that God must individually choose which humans will be saved and that He supernaturally regenerates the hearts of those He wants to save. Only those individuals hearts that He chooses to regenerate are then given the will to repent and turn to Christ. But this was initially based on God’s will and not their own. This idea is summed up in the phrase:  Regeneration Precedes Faith

For as many leading Calvinists say, “Calvinism can be summarized with the simple phrase: ‘Regeneration Precedes Faith’”. This order of salvation is at the heart of what differentiates Calvinism from everyone else. Does Regeneration Precede Faith (Calvinism) or does Faith Precede Regeneration (Biblical).

To those who are reading who may be new to these terms, this distinction may be surprising. It is the defining characteristic of Calvinism that with Total Depravity, only if God chooses to first regenerate your heart and give you the desire to repent can anyone then choose to turn from their ways and respond positively to his call to turn to Jesus. Only the elected few who he has chosen to grant this initial regenerated spirit, and make alive, have any hope for salvation. The Calvinists who also adhere to Irresistible Grace would continue this line of thinking in that those lucky few whom God regenerates, will be unable to choose anything other than to turn to God.

Who then does the saving

Non-Calvinists assert that it is because we cannot save ourselves that we must actively accept the gospel and turn to Christ for salvation. We still believe that all of the saving work is 100% done by Christ, and nothing we do can assist in our redemption, but God has ordained it to be man's responsibility to accept Christ's work on the Cross through the gospel which is sufficient to do that which it was set out to accomplish.

We believe the Gospel, in itself, is fully sufficient to accomplish what it sets out to do and does not require an additional grace to make it effective.

The Gospel is the sufficient means in which God initiates reconciliation to mankind.

It is important to note that every Christian should affirm Human Depravity, No one is righteous no not one, for all like sheep have fallen away. There is no Human aside from the Son of Man that is righteous. We affirm that man has fallen short and we are depraved, there is nothing we can do on our own accord to make up our sin to our Holy God. But because of his great love for us, the Father has provided a way to him through sending his Son Jesus to die on the Cross for our sins. The gap between God and mankind was 100% filled by Christ and he did all the work. The only thing he requires of us is Faith in Christ. Non-Calvinist will try and split hairs and say that if we even have faith then we have done a little bit of the work to take away from God's glory; however, Paul explicitly points out that faith is not a work, and thus, this is how humanity can be responsible to accept Christ by faith and we can still understand Christ does 100% of the work.

Our depravity doesn't make us blind to the gospel, it makes us in need of the Gospel.