"You were dead in the trespasses and sins."
Calvinism starts with a view of a spiritually-dead man, in whom God works by His sovereign grace to renew, regenerate, and justify. The various stripes of anti-Calvinist Christianity hold to a spiritually-able man who works his way to a relationship with God. To paraphrase, free-will Christianity teaches that a man is sick in trespasses and sins, while the Calvinist agrees with the Apostle Paul that the natural man is dead, completely unable to help himself spiritually.
In contrast to free-will Christianity, the Bible teaches that all of the initiative in salvation belongs to God, and none to man. Ezekiel 36:26 tells us, "I will give you a new heart, and a new spirit I will put within you. And I will remove the heart of stone from your flesh and give you a heart of flesh." That is, God changes our hearts, from the dead heart described in Ephesians, to a new living heart. And verse 27 continues, "And I will put My Spirit within you, and cause you to walk in My statutes and be careful to obey My rules." Now that He has given us a new heart, He sends His Holy Spirit to work in it, leading and enabling us to obey Him. For, as Jesus Himself says, "no one can come to me unless the Father who sent Me draws him" (John 6:44). Unlike the free-willer, God says that we are unable to seek Him, so He draws us to Him by His own will and power.
But we believe and are then saved, right? Nope. Jesus died for us while we were still in our sins (see, for example, Romans 5:6, I Peter 3:18). We aren't saved because we believe; we believe because we are saved! But our part in salvation is to have faith, right? Nope, wrong again. Ephesians 2:8, "For by grace you have been saved through faith. And this is not your own doing; it is the gift of God." Even our faith, our response to what Christ has done, is given to us by God. And John 1:13 says that Christians are "born, not of blood nor of the will of the flesh nor of the will of man, but of God."
But I know the free-willer is still holding on to his dream of contributing to his salvation. He's asking, "Alright, but I take it from there in my sanctification, right?" Nope, not that, either. Philippians 2:13, "for it is God who works in you, both to will and to work for His good pleasure." God's sovereign grace continues its work in us, conforming us to the holiness of Christ. As Paul also says in I Corinthians 15:10, "by the grace of God I am what I am, and His grace toward me was not in vain. On the contrary, I worked harder than any of them, though it was not I, but the grace of God that is with me."
Only Calvinism is consistent with the teachings of Scripture that man is utterly helpless in his own salvation. Rather, it occurs - in every step - by God's grace and Holy Spirit.