Some things we think we know, when we actually don’t. Our emotions, for example, tell us things that appear to be as right as rain, but have no basis in reality. Scripture offers us a true vision.
“As a result of all this, my loved brothers and sisters, you must stand firm, unshakable, excelling in the work of the Lord as always, because you know that your labor isn’t going to be for nothing in the Lord” 1 Cor 15.58 CEB.
We are able to stand firm and to excel in the Lord’s work because of what we know. That knowledge mentioned above was revealed—or reaffirmed—in chapter 15, about the truth of the resurrection.
Earlier, Paul lamented the existence of some among the Corinthians who “have no knowledge of God” v. 34. That was shameful, he said! (Part of the “work of the Lord” is helping the ignorant gain knowledge.)
The gospel contains essential content which must be fully accepted and assimilated. Once its truth has been understood, it provides staying power to the saint and motivation to keep working, because in the resurrection, it will all be worth it.