Without Irresistible Grace, perhaps better called the “effectual call,” no sinner would believe. Salvation would be impossible.
It is clear from the Bible that the Spirit’s regenerating work always precedes and causes faith. Jesus stated this to Nicodemus: “Unless one is born again he cannot see the kingdom of God” (John 3:3). This is reflected more or less clearly in every conversion recorded in the New Testament. An excellent example is the conversion of Lydia, which Luke records by writing, “The Lord opened her heart to pay attention to what was said by Paul” (Acts 16:14). Likewise, Jesus ascribed Peter’s great confession not to the operations of his flesh but to divine grace: “Flesh and blood has not revealed this to you, but my Father who is in heaven” (Matt. 16:17).
Regeneration—the new birth—precedes faith, so that prior to being born again it is impossible for anyone to believe on Jesus. Paul explains why: “The natural person does not accept the things of the Spirit of God, for they are folly to him, and he is not able to understand them because they are spiritually discerned” (1 Cor. 2:14). Therefore, if regeneration had to result from faith—if unregenerate sinners had to believe in order to be saved—then according to Paul, no one would ever be regenerated and saved. Instead, the Bible uniformly teaches what our sinful condition demands: regeneration precedes and causes saving faith. The apostle John put it succinctly: “Everyone who believes that Jesus is the Christ has been born of God” (1 John 5:1).
—Richard D. Phillips, What’s So Great about the Doctrines of Grace? (Reformation Trust, 2008), 76–77.