2 Corinthians 4:16 Therefore, we do not lose heart. Though outwardly we are wasting away, yet inwardly we are being renewed day by day. 

As we all can attest to, no matter what we do, we are outwardly wasting away.  However, God tells us not to lose heart, because inwardly we are being renewed day by day.  Also, Chapter 5 tells us we are looking forward to a new glorious body spending eternity with Jesus. This inward renewal also results in eternal rewards.  Personally, I believe this earthly renewal also impacts our heavenly assignments.  Thus, we should take this inward renewal seriously.  2 Corinthians 3:18, tells us how to participate in this inward renewal.

2 Corinthians 3:18 And we all, with unveiled face, beholding the glory of the Lord, are being transformed into the same image from one degree of glory to another. For this comes from the Lord who is the Spirit.  By beholding Jesus, reading the Bible, praying, obeying, we are being transformed.