What does 1 Corinthians 15:58 mean?
Having completed the main thrust of his letter, Paul brings his instruction and teaching to a formal conclusion. In the following, final chapter of 1 Corinthians, he will turn his attention to several assorted issues. Considering all he has written to them, he urges the Corinthians to be strong and faithful. More specifically, he tells them he loves them, referring to them as beloved brothers. Then he gives them several quick, uplifting commands."Be steadfast." Paul wants them to be faithful to the Lord and to his teaching about the Lord, to keep going.
Be "immovable." Paul is very concerned about the Corinthians' tendency to compromise their behavior and even their beliefs for the sake of the culture in which they live (1 Corinthians 10:13–14).
Be "always abounding in the work of the Lord." Paul has been clear that God gives each believer ways in which to serve Him, by serving each other in the church (1 Corinthians 12:4–11). The Corinthians should be doing so with enthusiasm. This work they do for the Lord is guaranteed to continue to matter for eternity, compared to so much of life that will cease to have meaning in years, days, or even minutes.
Even after all the issues Paul has tackled in this letter, including all the varied ways the Christians in Corinth were misunderstanding God's will and mistreating each other, Paul identifies them as belonging to the Lord. At no time is their salvation cast in doubt because of these misconceptions. Paul is convinced they are in Christ. They will one day be resurrected to new, glorified bodies in which they will spend eternity with the Father. Paul remains confident in the grace of God, because of the Corinthians' faith in Christ, and despite their failings.