2nd Corinthians 4:6-7 (see also John 1:9)
For God, who said, “Light shall shine out of darkness,” is the One who has shone in our hearts to give the light of the knowledge of the glory of God in the face of Christ. But we have this treasure in earthen vessels, that the surpassing greatness of the power may be of God and not from ourselves.
John Calvin comments: “For there is first the enlightening of the Gospel and then also that secret enlightening which takes place in our hearts.” (Calvin’s Commentaries: II Corinthians, Timothy, Titus, Philemon, p.57, emphasis mine)
What is this “secret enlightening,” to which Calvin refers?
Calvin explains: “For as in His creation of the world God has poured forth upon us the brightness of the sun and has also given us eyes with which to receive it, so in our redemption He shines forth upon us in the person of His Son by His Gospel, but that would be in vain, since we are blind, unless He were also to illuminate our minds by His Spirit. Thus his meaning is that God has opened the eyes of our understanding by His Spirit to make us able to receive the light of His Gospel.” (Calvin’s Commentaries: II Corinthians, Timothy, Titus, Philemon, p.57, emphasis mine)
Calvin infers that the preaching of the Gospel is “in vain” apart from the Calvinist belief that certain people are preemptively made Born Again in order to believe. First of all, prior to repentance, no one is made Born Again. A person must first hear and believe in the Gospel before he is sealed in Christ, as per Ephesians 1:13. However, this definitely sheds light on the Calvinist perspective of evangelism. To the Calvinist, the preaching of the Gospel is vanity, unless God sovereignly regenerates someone, and if God does in fact sovereignly regenerate someone, then there is nothing that can stop them from believing. Thus, the role of an evangelist is pure pageantry. In contrast, to the Arminian, the Gospel has power, as per Romans 1:16, through which the Holy Spirit kicks, pricks and convicts the lost.