Therefore we do not lose heart, but though our outer man is decaying, yet our inner man is being renewed day by day.
You are comprised of at least two major parts: your material self and your immaterial self. The outer man is your physical body, and the inner man is your soul/spirit which includes the ability to think, to feel, to choose (mind, emotions and will are often collectively identified as the soul), and to relate to God (spirit). Your body is in union with your soul/spirit, and that makes you physically alive. As a Christian, your soul/spirit is in union with God as a result of your conversion, and that makes you spiritually alive.
When God created Adam, he was totally alive--physically and spiritually. But because of Adam's sin and subsequent spiritual death, every person who comes into the world is born physically alive but spiritually dead. Being separated from God, you lacked the presence and wisdom of God in your life, so you learned to live independently of God, centering your interests on yourself. This learned independence from God is characteristic of the flesh or the old nature.
When you were born again, your soul/spirit was united with God and you came alive spiritually, as alive as Adam was in the garden before he sinned. As the epistle of Epheisans repeatedly declares, you are now in Christ, and Christ is in you. Since Christ who is in you is eternal, the spiritual life you have received from Him is eternal. You don't have to wait until you die to get eternal life; you possess it right now!
Our hope does not lie in the preservation of the outer man. It lies in the developing nature of the inner man. Our soul is in union with God and we are being renewed day by day. We will eventually lose our physical life, but not our spiritual life. Our emphasis should be on what is eternal, not on what is temporal.
Prayer: Lord, I won't lose heart over the setback in my life today because my hope lies in my eternal union with You.