Paul knew that the outward man or woman was perishing, day by day, and as he said “was wasting away” but the most important work was being done inwardly by the Spirit of God and this was the renewal that each believer in Christ is undergoing, day by day. God’s Spirit works to convict us of sin, He works to make us more like Christ, and our sanctification is a lifelong process and even though we might be falling apart outwardly, what is eternal is what is inside and that’s the only thing that counts. We are new creations in Christ (2 Cor 5:17) even though the outward appearance is decaying, so that’s why Paul didn’t want us to lose heart.
A godly marriage may not change the ‘world ‘ in terms of it’s influence doctrinally …but wait….why then does the Lord exhort those in marriage to prepare to love their wives and thus as you have shared ..the wife will find it much easier to respond ..as God loved us first …so we love HIM ..the husband initiates love and so his wife will find it easier to love and follow him. Bible Verse Wall Art