1 Corinthians 15:14, 58
1 Corinthians 15:14 ESV
And if Christ has not been raised, then our preaching is in vain and your faith is 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.