When God called the world into being, the universe did not hesitate to comply with the command. God's desired effect in creation came to pass. Likewise, when Jesus called the dead Lazarus from his grave, Lazarus responded with life.
There is also an effectual call of God in the life of the believer. It is a call that brings about its desired effect, Effectual calling is related to the power of God in regenerating the sinner from spiritual death. It is sometimes referred to as "irresistible grace."
Effectual calling refers to a call of God that by His sovereign power and authority brings about His designed and ordained effect, or result. When Paul teaches that those who He predestined, He calls, and those whom He calls, He justifies, the call which he is referring is the effectual call of God.
The effectual call of God is an inward call. It is a secret work of quickening or regeneration accomplished in the souls of the elect by the immediate supernatural operation of the Holy Spirit. It effects or works the inward change of the disposition, inclination, and desire of the soul. Before the inward effectual call of God is received, no person is inclined to come to Him. Everyone who is effectually called is now disposed to God and responds in faith. We see, then, that faith itself is a gift from God, having been given in the effectual call of the Holy Spirit.
The preaching of the gospel represents the outward call of God. This call is heard audibly by both the elect and the nonelect. Human beings have the ability to resist and refuse the outward call. He will not respond to the outward call in faith unless or until the outward call is accompanied by the effectual inward call of the Holy Spirit. Effectual calling is irresistible in the sense that God sovereignly brings about its desired result. This sovereign work of grace is resistible in the sense that we can and do resist in our fallen nature, but irresistible in the sense that God's grace prevails over our natural resistance to it.
Effectual calling refers to the creative power of God by which we are brought to spiritual life. The Apostle Paul writes:
And you were dead in the trespasses and sins in which you once walked, following the course of this world, following the prince of the power of the air, the spirit that is now at work in the sons of disobedience—among whom we all once lived in the passions of our flesh, carrying out the desires of the body and the mind, and were by nature children of wrath, like the rest of mankind. But God, being rich in mercy, because of the great love with which he loved us, even when we were dead in our trespasses, made us alive together with Christ (Ephesians 2:1-5).
We who were once children of wrath and were spiritually dead have become the "called out ones" by virtue of the power and efficacy of the inward call of God. In His grace, the Holy Spirit gives us eyes to see what we would not see and ears to hear what we would not hear.
Adapted from the Reformation Study Bible
Salvation by Grace: The Case for Effectual Calling and Regeneration by Matthew Barrett