1 Corinthians 15:2, 58
1 Corinthians 15:2 ESV
and by which you are being saved, if you hold fast to the word I preached to you—unless you believed in vain.
1 Corinthians 15:58 ESV
Therefore, my beloved brothers, be steadfast, immovable, always abounding in the work of the Lord, knowing that in the Lord your labor is not in vain.