“Now then we are ambassadors for Christ, as though God did beseech you by us: we pray you in Christ’s stead, be ye reconciled to God…We then, as workers together with Him, beseech you also that ye receive not the grace of God in vain” (2 Cor. 5:20, 6:1).
We have a privilege by grace to be workers together with God, and we have a privilege by grace to be Christ’s ambassadors. By the grace of God, each person reconciled to God is called to beg people to be reconciled to God. Our reconciliation with God puts each of us into the ministry of reconciliation (5:18).
However, not all in Corinth were doing this. They missed their ministry. “Vain” means empty, useless, fruitless, without effect or purpose. Receiving the grace of God “in vain” is the opposite of 2 Corinthians 5:15: “And that He died for all, that they which live should not henceforth live unto themselves, but unto Him which died for them, and rose again.”
When believers live for themselves only, rather than for the purposes to which God has called them, that’s receiving the grace of God in vain. Gratitude for God’s grace is to make us want to live for and work for the One Who gave everything for us, Who died for us, and saved us from eternity in the Lake of Fire.
We have a stewardship, a responsibility, a duty as ambassadors for Christ. To receive the grace of God in vain is not teaching that the salvation of the Corinthian believers was in jeopardy; it is teaching that the salvation of other people was in jeopardy.
In these verses, God begs the believer to live as a bright gospel light out of care for people around us and their eternal destinies. Receiving the grace of God in vain is to live a life without aim or meaning. But when the grace of God is received and touches your heart, it gives you purpose, a gospel mindset, and you see the vital importance to be a light and to live for what is important to God. source