1st Timothy 1:15-16 (see also Romans 5:8; 1st Corinthians 15:9)
It is a trustworthy statement, deserving full acceptance, that Christ Jesus came into the world to save sinners, among whom I am foremost of all. Yet for this reason I found mercy, so that in me as the foremost, Jesus Christ might demonstrate His perfect patience as an example for those who would believe in Him for eternal life.
George Bryson comments: “I take this to mean that if you are a sinner, He came to save you.” (The Dark Side of Calvinism, p.167, emphasis mine)
J. Vernon McGee comments: “Under the Law the best man in the world is absolutely condemned, but under the gospel the worst man can be justified if he will believe in Christ.” (Thru the Bible commentary series: First and Second Timothy, Titus and Philemon, p.27, emphasis mine)
James Leonard explains: “Paul seems to delimit sinners as the object of Christ’s saving by pointing to himself as the worst possible example of them. The implied argument is that if Jesus came to save Paul, then surely Christ came to save everyone. The point is emphasized by Paul’s employment of the faithful saying refrain, with the additional qualification that it is worthy of all acceptance. In retrospect, it is easy to imagine that Paul felt his point needed this additional emphasis precisely because a certain element within Ephesus was posing some sort of soteriological elitism. Perhaps this may also explain Paul’s enigmatic appeal to his ignorance as the basis for God’s outpouring of his grace, an excuse which is otherwise rejected elsewhere in his writing. The point then, would be that even those who do not have knowledge have access to the free grace of God—and this might have been posed polemically against the shipwrecked teachers of Ephesus.” (Soteriological Elitism in the Pastoral Epistles, emphasis mine)
John Calvin comments: “When Paul turned from being a wild attacking beast into a shepherd and pastor, Christ showed his grace in a special way. It demonstrated that the way of salvation is open to everyone, no matter how notorious sinners they might have been previously.” (1 & 2 Timothy & Titus: Calvin, The Crossway Classic Commentaries, p.28, emphasis mine)
“Everyone”? Is that what Calvin just said? Well if Jesus only died for some people, according to the Calvinistic Doctrine of Particular Redemption (or Limited Atonement), how can salvation be “open to everyone”? Is it “open” to those whom Christ, allegedly, did not die for? How could salvation be “open” to those whom payment was allegedly never made? (As a side note, Calvin abandoned the Doctrine of Limited Atonement).
John Calvin writes: “That Christ, the redeemer of the whole world, commands the Gospel to be preached promiscuously to all does not seem congruent with special Election. ... But the solution of the difficulty lies in seeing how the doctrine of the Gospel offers salvation to all. That it is salvific for all I do not deny. But the question is whether the Lord in His counsel here destines salvation equally for all.” (Concerning the Eternal Predestination of God, pp.102, 103, emphasis mine)
Calvin adds: “It is incontestable that Christ came for the expiation of the sins of the whole world.” (Concerning the Eternal Predestination of God, p.148, emphasis mine)
Besides 1st John 2:1-2 referenced in Calvin’s quote, 1st Timothy 1:15 also makes a strong case.