God designed marriage as one of the most public displays of His plan and purposes for the world to see. We are to go out and live in a dark and hopeless world, chasing after elusive pleasures, and never finding lasting satisfaction: and RADIATE Christ.
When God set the curriculum for His Church, thus is what He chose to be taught. In simple words that everyone alive in the First Century church could comprehend, Paul wrote to Titus. The early believers of Crete not only understood, but they had a picture of this quality burned into their mind from the Roman culture alive and moving all around them.