This second time Art took us to being the salt of the earth and why we should live conspicuously Christian lives in a culture that despises Christians. The sermon on the mount demands engagement from believers in this world, we are indeed indispensable to to the world's highest welfare.
His three points included a negative insinuation (earth is decomposing), a positive declaration (seemingly insignificant we are to preserve the earth) and a devastating evaluation (if we deny our function we will lose our invalidate ourselves). Under the second heading he spoke of the tension between gospel effectiveness through intimate engagement and remaining distinct and not allowing the salt to lose its flavour.
I think this is what he was trying to get over when he was the main speaker here some years back. The devil, of course, is in the detailed working out.