In reading Nancy Duarte's HBR Guide to Persuasive Presentations, Duarte refers to messages having STAR moments. The acronym STAR referring to "Something They Always Remember."
When preparing and delivering talks to young adult and teenage audiences, this piece of advice is even more crucial. Whether the STAR quality is an unforgettable visual, a story, or even a token they take home, it is vitally important for the "stickiness" of your message.
Recently, we did a message called "What's in Your Box?" where we focused on all of the various "stuff" that each of us carries around inside our little "box" and try to keep hidden from others. The message closed with James 5:16 (confess your sins and pray for each other) and the students were encouraged to come to the front, grab a small box, and find someone to open their box to and share what is hidden inside (sin, failure, mistakes, suffering, etc). Afterward, the students took their boxes home and were encouraged to put them in a prominent place in their room where they would be reminded to continue to live their lives "open" with one another.
Whereas many students (and most adults for that matter) walk away from a message and forget what they have heard fifteen minutes later, you want to leave them with something they will never forget. Not only will it reinforce the principle or scripture that you are trying to teach, but will be a STAR that they (or the Holy Spirit) can draw upon months, years, or even decades later.