The following is an excerpt from The MacArthur New Testament Commentary on 2 Corinthians 6.

we also urge you not to receive the grace of God in vain—for He says, “At the acceptable time I listened to you, and on the day of salvation I helped you.” Behold, now is “the acceptable time,” behold, now is “the day of salvation”— (6:1b–2)

Paul’s use of the verb parakaloumen (urge; “plead”; “beg”) in the present tense reflects his constant, passionate concern for the Corinthians (cf. 2:8; 10:1; 1 Cor. 16:15–16). God’s ambassadors are privileged pleaders, begging their hearers to respond to the truth.

Specifically, Paul was urging the Corinthians not to receive the grace of God in vain; not to turn away from the gracious opportunity to hear the gospel of forgiveness he had so faithfully preached to them. He had poured his life into the Corinthians during his long stay in their city (Acts 18:11), pleading with them for the gospel and teaching the new converts how to grow in grace. But events in Corinth caused the apostle to fear that his intense labor had been for nothing. The church was riddled with sin, as Paul’s first inspired epistle to them reveals. False teachers, those wolves in sheep’s clothing both Jesus (Matt. 7:15) and Paul warned of (Acts 20:29), were luring many in the assembly away from the truth. This passionate concern for the Corinthians was behind what he wrote later:

But I am afraid that, as the serpent deceived Eve by his craftiness, your minds will be led astray from the simplicity and purity of devotion to Christ. For if one comes and preaches another Jesus whom we have not preached, or you receive a different spirit which you have not received, or a different gospel which you have not accepted, you bear this beautifully. (2 Cor. 11:3–4)

Paul could not stand idly by and allow his diligent efforts to be undone. He could not permit his spiritual children (1 Cor. 4:15) to be deceived by a false gospel or led astray from the true path of sanctification. His duty before God, like that of all faithful ministers, was to exhort people not to receive the grace of God in vain. The apostle had given them the grace of God, as embodied in the truth of the gospel of grace, for their eternal benefit.

Paul was concerned first that the Corinthians not receive God’s grace in regard to salvation in vain. As in any church, not everyone in the Corinthian assembly was redeemed. Some had intellectual knowledge of the gospel but did not have saving faith. That is why Paul challenged them, “Test yourselves to see if you are in the faith; examine yourselves! Or do you not recognize this about yourselves, that Jesus Christ is in you—unless indeed you fail the test?” (2 Cor. 13:5). Those in the congregation who were not regenerate were in grave danger of being deceived by the false teachers. To follow those preaching another Jesus, another Spirit, and another gospel would lead to a waste of their privilege and to spiritual ruin. Paul was similarly concerned about the Galatians:

I am amazed that you are so quickly deserting Him who called you by the grace of Christ, for a different gospel; which is really not another; only there are some who are disturbing you and want to distort the gospel of Christ. But even if we, or an angel from heaven, should preach to you a gospel contrary to what we have preached to you, he is to be accursed! As we have said before, so I say again now, if any man is preaching to you a gospel contrary to what you received, he is to be accursed! (Gal. 1:6–9)

The Corinthians were also in danger of receiving God’s grace in vain with regard to sanctification. The legalists sought to turn them away from living in the power of the Spirit to living in the strength of the flesh. Paul chided the Galatians, also under assault by legalism, “Are you so foolish? Having begun by the Spirit, are you now being perfected by the flesh?” (Gal. 3:3). Sanctification, like justification, is a work of God. It does not come from legalistically conforming to an external set of rules but from a Spirit-generated, heartfelt love for and obedience to the Lord Jesus Christ.

Some of the unsaved Corinthians were being led astray by a false gospel of salvation by works. Others were saved, but legalistic false teaching was stunting their spiritual growth. In either case, the grace of God to them that sent Paul with the gospel was in danger of being nullified.

The corrupting influence of the false teachers hindered evangelism. That made the Corinthians’ defection all the more galling to Paul, for it was (and still is) the time for the ministry of reconciliation. To stress the urgency of this time, Paul quoted from Isaiah 49:8, where God declared, “At the acceptable time I listened to you, and on the day of salvation I helped you.”

There is a time in God’s grace when He may be sought by sinners. The Lord warned the pre-Flood world, “My Spirit shall not strive with man forever, because he also is flesh; nevertheless his days shall be one hundred and twenty years” (Gen. 6:3). Isaiah 55:6 commands, “Seek the Lord while He may be found; call upon Him while He is near.” Hosea warned that apostate Israel “will go with their flocks and herds to seek the Lord, but they will not find Him; He has withdrawn from them” (Hos. 5:6).

Repeating behold and now to emphasize his point, Paul declared that now is “the acceptable time,” “the day of salvation”   when God will listen to repentant sinners. Now, when the fields are ripe for the harvest (John 4:35), is not the time to waste gospel opportunity, or to be feeble, vacillating, or deceived by false teachers. It is the time to hold fast to the truth and faithfully proclaim it. “We must work the works of Him who sent Me as long as it is day,” Jesus admonished. “Night is coming when no one can work” (John 9:4).

Knowing the urgency of the times Paul, true to the urgency of his calling, passionately pleaded with the Corinthians not to let God’s grace in their lives be in vain.