The infinitive "to receive" (δέξασθαι) means to receive a gift from someone or to receive someone into your home (BAGD, p.177). Paul uses the word in 2 Corinthians 7:15 to describe the reception the Corinthian church gave to Titus, his messenger. The negative particle (μὴ) goes with the infinitive rather than the verb "appeal" (παρακαλοῦμεν) because οὐκ is used with indicatives while μὴ is used with the other moods (BAGD, p.590). The sense is "we appeal to you not to receive" as opposed to "we do not appeal to you to receive." The phrase translated "in vain" (εἰς κενὸν) means without result, without reaching its goal. God's grace is empty and achieves no purpose (BAGD, p.427) if it is received in vain.
Is it even possible to receive the grace of God in a way that proves to be ineffective? Philip Hughes raises that question and then summarizes the four ways that this phrase is interpreted (Hughes, 2 Corinthians, pp.217-219). 1) Paul is talking about receiving God's grace in a purely external and superficial manner. Such a person is a professing Christian but not a true believer. However, the context makes it unlikely that Paul is talking about false professions of faith. 2) Paul is talking about a person who accepts God's grace only to reject it later. Such a person loses his salvation, thus receiving the grace in vain. This view flies in the face of Paul's statements elsewhere regarding salvation (e.g., Phil. 1:6) 3) Paul's appeal is not directed toward the Corinthians but to the world in general to whom God offers His reconciliation. Paul appeals to the world not to reject this great salvation. In this view, people do not receive the grace in vain. They never receive it all. 4) Paul is talking about Christians when they stand before the Judgment Seat of Christ (2 Cor. 5:10)
The best interpretation is the fourth view. To receive the grace of God in vain is to live in ways that are inconsistent with grace. Our practice does not match our doctrine. Here we go back to the meaning of the word "vain" (κενὸν) above. The grace of God does not produce the intended results in our lives. Our actions constitute a denial of the truth. When we stand before Christ's judgment seat (the evaluation of believers not unbelievers), our actions will prove to be empty of eternal value. The purifying fire of God's judgment will consume the wood, hay, and stubble in our lives although we will be saved "as through fire" (1 Cor. 3:10-15).
Paul writes these words in the context of a great parenthesis in his letter (2 Cor. 2:14 - 7:4) dealing with sin and conflict in the body. He exhorts them to forgive the sinful offender before the parenthesis and then commends them for that forgiveness after the parenthesis (2 Cor. 2:7, cf. 2 Cor. 7:12). The conflict includes Paul who has felt alienated from the people in Corinth (2:2:13, cf. 7:5-16). Reconciliation is meant to transform our relationships. If we are reconciled to God by His grace, then we should be reconciled to one another as well. If we are not reconciled with one another, then we have received God's grace in vain. In this case, His reconciling grace serves no purpose in our lives (Martin, 2 Corinthians, p.166).
Horizontal reconciliation proves we have not received vertical reconciliation in vain!
