by J. I. Packer
.... From the beginning God chose you to be saved through the sanctifying work of the Spirit and through belief in the truth. He called you to this through our gospel, that you might share in the glory of our Lord Jesus Christ. 2 THESSALONIANS 2:13-14
Effectual calling is a sixteenth-century English phrase that became the title of chapter X of the 1647 Westminster Confession. The chapter begins thus:
All those whom God hath predestinated unto life, and those only, he is pleased, in his appointed and accepted time, effectually to call, by his Word and Spirit, out of that state of sin and death, in which they are by nature, to grace and salvation, by Jesus Christ; enlightening their minds spiritually and savingly to understand the things of God, taking away their heart of stone and giving unto them a heart of flesh; renewing their wills, and, by his almighty power, determining them to that which is good, and effectually drawing them to Jesus Christ: yet so, as they come most freely, being made willing by his grace.
What is being spoken of here is the many-sided reality of Christian conversion, involving illumination, regeneration, faith, and repentance. It is being analyzed as a sovereign work of God, “effectually” (i.e., effectively) performed by the power of the Holy Spirit. The concept corresponds to Paul’s use of the verb call (meaning “bring to faith”) and called (meaning “converted”) in Romans 1:6; 8:28, 30; 9:24; 1 Corinthians 1:24, 26; 7:18, 21; Galatians 1:15; Ephesians 4:1, 4; and 2 Thessalonians 2:14, and contrasts with the idea of a merely external and ineffective invitation, as found in Matthew 22:14.
Original sin renders all human beings naturally dead (unresponsive) to God, but in effectual calling God quickens the dead. As the outward call of God to faith in Christ is communicated through the reading, preaching, and explaining of the contents of the Bible, the Holy Spirit enlightens and renews the heart of elect sinners so that they understand the gospel and embrace it as truth from God, and God in Christ becomes to them an object of desire and affection. Being now regenerate and able by the use of their freed will to choose God and the good, they turn away from their former pattern of living to receive Jesus Christ as Lord and Savior and to start a new life with him.
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From: Concise Theology: A Guide To Historic Christian Beliefs