The chapel must be relevant and there is no better way to achieve it than clearly, emphatically declare God's Law.
C.F.W. Walther, the Lutheran Church Missouri Synod's first president stated in his book, The Proper Distinction Between Law and Gospel that , “…the Law uncovers to man his sins, but offers him no help to get out of them and thus hurls man into despair.
In the third place, the Law does indeed produce contrition. It conjures up the terrors of hell, of death, of the wrath of God. But it has not a drop of comfort to offer the sinner. If no additional teaching, besides the Law, is applied to man, he must despair, die, and perish in his sins. Ever since the Fall the Law can produce no other effects in man. Let us ponder this well.”
That's as relevant as it gets. We all have sinned and the condemnation of the law must be clear. The condemnation of the Law makes it clear that we are all in need of saving. The time period matters not. We are as sinful as the both thieves on the cross. The penalty for our sins is death. That message may vary in approach but must not vary in meaning.
Once we understand the situation we are in because of our sinful existence, we understand the need for an external agent to save us. God in his abundant grace gave us this external agent in His son, who did what we could never do. Christ paid the penalty for our sins and cleansed us from the damnation made so clear in the Law.
C.F.W. Walther describes the Gospel this way. "The effects of the Gospel are of an entirely different nature. ...The second effect of the Gospel is that it does not at all reprove the sinner, but takes all terror, all fear, all anguish, from him and fills him with peace and joy in the Holy Ghost. At the return of the prodigal the father does not with a single word refer to his horrible, abominable conduct. He says nothing, nothing whatever, about it, but falls upon the prodigal’s neck, kisses him, and prepares a splendid feast for him. That is a glorious parable exhibiting to us the effect of the Gospel. It removes all unrest and fills us with a blessed, heavenly peace.
In the third place, the Gospel does not require anything good that man must furnish: not a good heart, not a good disposition, no improvement of his condition, no godliness, no love either of God or men. It issues no orders, but it changes man. It plants love into his heart and makes him capable of all good works. It demands nothing, but it gives all. Should not this fact make us leap for joy?"
Back to relevance. Relevance can't simply be defined as meeting the audience with cultural connections. If that's all it is the chapel message falls short. The relevance of the Law and Gospel transcends time and must be present in all chapel messages.