The day will come when we will stand before the Lord Jesus Christ. Any ideas what you will say to Him? What will be your boast about your relationship to others in His Church? Are you able to rejoice in the ministry you have received? Will the things you say then match what you say now about the church?
Paul’s attitude toward this church is not the same as the attitude this church has for Paul. They misunderstood Paul so they wrote him off. Paul prayed and gave thanks for them (1 Cor 1:4-9). Paul had already referred to the Day of the Lord Jesus 3 times in the previous letter, so this does not catch them (or us) by surprise.
The day he refers to is not a day when a person’s salvation is decided, whether one gets to enjoy God forever (eternal life) or receive the just reward of eternal punishment for sin. Rather, the day Paul refers to here is the day followers of Christ see Him face to face by means of resurrection or rapture.
How does God see your heart? Do your words and works match . . . now, or will Jesus our Judge match them for us later? Have a clear conscience as you interact with people before God.