As Paul draws close to the end of his letter to the church at Corinth, he wants to stress the importance of knowing that we have victory in Jesus Christ and that our work for Him will not be in vain.
As Christians, we need to be solid as a rock. Our foundation needs to be firm. We cannot be moved by things like temptation or sadness or wicked desires... We have to stay grounded and steadfast in our faith and in our actions.
Sometimes, it's easy to think, "What am I even striving toward... I'm putting forth so much effort and not seeing any results." - Paul knew there were going to be people who felt this way - that's why he wants to stress the fact that our labor for God is not in vain and the things we do for Him will not go unnoticed.
We need to be Christians who are grounded in our faith and will stand strong in the face of whatever comes our way.