"Therefore, my beloved brethren, be steadfast, immovable, always abounding in the work of the Lord, knowing that your toil is not in vain in the Lord."
Paul concludes his 1 letter to the Corinthians with this verse. He was trying to encourage the Corinthians to be steadfast to the end. Though they would face many trials and troubles as they lived out their Christian faith in the city of Corinth, which was known for its pagan idolatry, their labor would not be in vain.
I know sometimes when I am doing ministry, I wonder if my labor is in vain. We try to reach people with the gospel and sometimes we feel as if certain people will never believe no matter what happens. This can be discouraging especially with those people we love and want to spend eternity with in heaven.
But Paul says in effect, "Don't lose heart! Stay rooted in the power of the resurrection. Always give your heart to the work of the Lord. Keep up the fight. Don't be moved. Stay rooted in Christ. Why? Because there is a crown laid up for you in heaven that will never fade away! Despite the sufferings you endure on earth, one day it will be worth it all. Paul says in Romans 8, "I consider the sufferings we face in this world are not worthy to be compared to the glory that will be revealed in us through Christ Jesus our Lord!"
Where does your work feel like it is being done in vain? Where are you tempted to give up with someone or some ministry because you just don't feel like you are making a difference? Remember that God is always at work through us in ways that we often can't see. Though we may not see the fruit of our labor on this side, God will always redeem what we do for His glory! Your labor is not in vain. Stay steadfast and immovable my friends it will be worth it all some day!