Therefore we do not lose heart, but though our outer man is decaying, yet our inner man is being renewed day by day.2 Corinthians 4:16(NASB)
Paul's church epistles were written to different groups of Christians, dealing with matters that were important to their need at the time, and yet they address issues that remain relevant today. Paul's letters were written as an integrated whole, yet progress from one train of thought to the next. Paul's writings were written to correct any error, preach a clear gospel message, provide encouragement, and address issues of concern.
Paul's passion was to reinforce the good news of the gospel with clarity and remind us that as part of God's new creation, we are aliens in a foreign land - living in deteriorating earthen vessels with a heavenly hope. As part of the Body of Christ, we are indwelled by the Spirit of God with an eternal inheritance - kept for us in heaven.
Having set the scene of our present privileged position and glorious future destiny in the first three chapters, Paul opens a section which calls Christians to stand fast in the evil day, to press on despite the difficulties we face, and to live by faith and not by sight: "We do not lose heart," are his inspiring words, "we don't give up or faint from fear," he continues, "for although our outer man is decaying, yet our inner man is being renewed day by day."
We are not to become discouraged or anxious. We are not to allow ourselves to become wearied or fearful. Although our physical bodies are growing older and we notice that our outer man is progressively decaying and wasting away, nevertheless, our inner self is being renewed day after day.
The new life we received at salvation is being transformed into the image and likeness of Christ, as we mature in the faith, grow in grace, and gain a more intimate knowledge of our Lord and Saviour, Jesus Christ.
It is only by God's grace we have received mercy for help in time of need, so we should not lose heart knowing that those who wait for the Lord will renew their strength and mount up with wings like eagles: "They will run and not grow weary. They will walk and not faint." God has promised to strengthen the weary through His sufficient grace, for we have put on the new self, which is being renewed to a true knowledge of Christ, according to the image of the One Who created us.
Paul joyfully concurred with the law of God relating to the inner man - that we are being renewed every day. He made it clear, in this verse, that he was ready and willing to undergo all kinds of suffering, sadness, difficulties, and dangers, for the certain hope we have in our glorious resurrection from the dead - when this mortal will put on immortality and this perishable body, that is progressively decaying and wasting away, will put on the imperishable - and it is all by grace through faith in Jesus Christ, our only God and Saviour.
Heavenly Father, what a wonderful hope we have in Christ that, day by day, we are being renewed in our inner man, even though we can see our outward body is growing older and deteriorating. Thank You for my present privileged position in Christ and for the glorious future destiny I have in heaven. I pray that I will not lose heart as I see my outer man decaying, but will stand strong in the faith and press on for the upward call of God in Christ Jesus, as I watch for His any day return when this mortal will put on immortality and this perishable body will be clothed in an imperishable one, for Your greater praise and glory. How I thank and praise You, in Jesus' name, AMEN.