Once you have been qualified and trained as a marine, you are considered to be a “leatherneck” forever. Which means, you are expected to live out the values and attitudes of a marine. The Marine Corps Officer’s Guide,” 1964 edition, makes it clear: “Traditions are not preserved by books and museums, but by faithful adherence on the part of all hands—you especially.” Translation? Since you are a marine, live like one.
Paul wrote something similar to fellow Christians:
Only let your manner of life be worthy of the gospel of Christ, so that whether I come and see you or am absent, I may hear of you that you are standing firm in one spirit, with one mind striving side by side for the faith of the gospel, without being frightened in any way by those who oppose you. – (Philippians 1:27-28a)
What does it mean to live a life “worthy of the gospel of Christ?” In this short quote, we see it means to confidently stand firm in what you believe without letting opposition sway you. It also means to be joined with other believers by the Spirit of God, operating on the same page and working together to spread the good news. With no fear.
In a team sports contest, you can generally pick the winner by observing which team plays with the most confidence and unity. Confidence and unified hearts and minds are the essentials as well for a life “worthy of the gospel.”