Grace as the power of God to save His elect cannot be resisted. The Spirit of God and the grace obtained for God's people through the work of His Son Jesus Christ is completely effectual and cannot be rejected by anyone whom God has chosen to be His own. By His grace and in the way of sanctification, God works in the hearts of his people a desire to love, seek, and obey Him.
Read more about the distinctive Reformed view of irresistible grace in this excerpt from the third chapter of Saved by Grace by Ronald Cammenga and Ronald Hanko.
The doctrine of irresistible grace, or "efficacious grace" as it is sometimes referred to, is the fourth of the Five Points of Calvinism. It is represented by the I in the acronym TULIP. Irresistible grace stands opposed to the teaching that salvation depends on the final decision of man. According to Arminianism, God's grace can be frustrated by man. Calvinism teaches that God's grace irresistible saves man.
By irresistible grace we mean that God's grace and salvation cannot be effectively resisted. When God determines to save a man, that man is saved! Neither that man himself nor the devil, nor the wicked world are able to prevent his salvation. Nothing can stand in the way of God's saving purpose. Not only does God will to save him and work to save him, but he actually does save him, "For who hath resisted his will?" (Romans 9:19).
Irresistible grace is an important issue. Let no church or individual Christian suppose otherwise. The importance of this issue is not merely that it concerns the question, "Can grace be resisted?" but ultimately the question, "Can God be resisted?" for the grace of salvation in God's grace. Can God, the sovereign God—the God about whom the Scriptures declare that "he doeth according to his will in the army of heaven...and none can stay his hand" (Daniel 4:35)—be frustrated in His will to save even one sinner? The issue concerns the very character and being of God. The doctrine of irresistible grace confronts us with the most fundamental question with which man can be faced: what do you believe about God?
Because the Reformed faith confesses the truth that God is a sovereign God, it also teaches that scriptural truth of His irresistible grace. This, surely, is rigorous logic, as any clear-thinking person can see. More importantly, this is the teaching of the Holy Scriptures...
It is plain that the power of grace must be a great power. Man is the sinner; God must be the Savior. Man is incapable; God must be able. Man is powerless; God must be omnipotent. Man is weak; God must be sovereign...
The saving of the sinner demands great power. The devil must be defeated; a rebel must be subdued; a heart of stone must be made a heart of flesh; a new creature must be brought forth; the dead must be raised. This work calls for great power, power that is beyond the power of a mere creature: miraculous power, supernatural power, divine power...
Grace, if it is grace, must be irresistible grace. Because God is an irresistible, powerful, and sovereign God, His grace is irresistible, powerful and sovereign. God and God's grace cannot effectively and ultimately be resisted by the most obstinate of sinners. When God's grace operates to save the sinner, that grace will triumph in the salvation of that sinner. He will be saved. God will have the victory. Not the power of the devil, not the power of the wicked world, not the power of the sinner himself, shall be able to prevent, overthrow, or frustrate the work of God's grace. The God of the Scriptures is the God of whom Isaiah says in Isaiah 46:10-11, "I am God, and there is none like me, Declaring the end from the beginning, and from ancient times the things that are not yet done, saying, My counsel shall stand, and I will do all my pleasure." he is the God before whom Daniel says in Daniel 4:35, "All the inhabitants of the earth are reputed as nothing: and he doeth according to his will in the army of heaven, and among the inhabitants of the earth: and none can stay his hand, or say unto him, What doest thou?"
The god of resistible grace is not the God of the Scriptures. The former is the weak god, an ineffective god, a powerless god. In reality, he is no god at all, but an idol. This is the seriousness of the denial of God's irresistible grace.