Therefore we do not lose heart. Though outwardly we are wasting away, yet inwardly we are being renewed each day. For out light and momentary troubles are achieving for us an eternal glory that far outweighs them all. So we fix our eyes not on what is seen, but what is unseen, since what is seen is temporary, but what is unseen is eternal.-2 Corinthians 4:16-18
Paul is telling us here to not give up. Why are we not to give up? Because we have something that those who have chosen to not follow Jesus do not have, and that something is hope. And the hope we have is the knowledge that even though this temporary shell we call a body is dying, that which lives inside us (our soul) cannot die and is being renewed each and every day. That is why Paul tells us to fix our eyes on those things that are unseen, which are the things that are good for our souls and our spirits, and not the those things that are seen, which are those things that are only good for attempting to make our bodies last forever. And it is the same reason the writer of Hebrews concluded his discussion on faith with these words:
Therefore, since we are surrounded by such a great cloud of witnesses, let us throw off everything that hinders and the sin that so easily entangles. And let us run with endurance the race marked out for us, fixing our eyes on Jesus, the pioneer and perfecter of faith. For the joy set before him he endured the cross, scorning its shame, and sat down at the right hand of the throne of God. Consider him who enduring such opposition from sinners, so that you will not grow weary and lose heart.-Hebrews 12:1-3 NIV
It is only when we fix our eyes on Jesus and what he has called us to do, that we find the necessary strength to carry on in the face of day to day opposition. It is through fixing our eyes on Jesus that we begin to see what Paul said in 2 Corinthians “For our light and momentary troubles are achieving for us an eternal glory that far outweighs them all” (2 Corinthians 4:17 NIV). So fix you eyes on Jesus and you will see what the prophet Isaiah saw.
Do you not know? Have you not heard? The Lord is the everlasting God, the Creator of the ends of the earth. He will not grow tired or weary, and his understanding no can fathom. He gives strength to the weary and increases the power of the weak. Even youths grow tired and weary, and young men stumble and fall; but those who hope in the Lord will renew their strength. They will soar wings like eagles; they will run and not grow weary, they will walk and not be faint.-Isaiah 40:28-31 NIV