1 Corinthians 1:8 (AV)
8 Who shall also confirm you unto the end, that ye may be blameless in the day of our Lord Jesus Christ.
Who shall also confirm points back to verse 7; it is the Lord Jesus Christ who shall confirm… Believers are confirmed to the end. The word “confirm” contains the word “firm”. That is exactly the meaning, to make firm.
Jesus Christ will make you firm in your faith until the day of our Lord Jesus Christ. Here, this day is the Rapture of the Church. The “day of Christ” relates wholly to the reward and blessing of believers and saints at his coming. Paul always uses the term “Day of Christ” in a positive sense. In contrast, the day of the LORD is always connected with judgment, darkness, and terror. The Corinthians could take heart in knowing the day of Christ would come first!
Those who adhere to a Calvinist doctrine or Lordship salvation are quick to accuse someone who is caught in sin as not being a true believer. You can be assured of your salvation even if you fall into sin (there is never any need to doubt!). If you have placed your trust in Jesus Christ he has made you firm in your faith!