John the Baptist announced the next level of the war between God and His enemies. The Savior born into this world was to be Satan's doom; John signaled the beginning of His ministry. This involved His death, as is common in war. Mark, the "action" Gospel, leaps in at this point. In the baptism of each Christian, a new member of God's army is enlisted.
But why does Isaiah tell the messenger, John, to tell Jerusalem (a city used to perpetual, literal war) that "her warfare is over"? Answer: the warfare was taken up by God incarnate. War's cost is ultimately life laid down. But don't let this event of utmost importance slip into distant memory (as Pearl Harbor has for many), then out!
John's mission was to elevate Christ and lower himself; our role is similar. Call attention to the Savior within us, the Bringer of true peace on earth, something more than Rudolph. Peace is possible only after war. Christ did what was needed; now we have life. The world doesn't get it, so show them! The battle with sin for life and death is over.
Have a blessed Advent! Sermons will be from my home church until February.