King David grew old, and no one could warm him (1 Kings 1:1). The doctors tried blankets. They tried attendants. His body, which had survived lions and bears and Goliath and armies and decades of war, had lost its inner fire. Ecclesiastes had the diagnosis: "No man has power over the spirit to retain the spirit; and there is no discharge in that war" (Ecclesiastes 8:8). When the time comes, the spirit blooms outward and departs. There is no holding it.
The rabbis of Aggadat Bereshit see David's old age as the completion of an arc that began with the angels. David had prayed for protection throughout his life — "He who dwells in the secret place of the Most High shall abide under the shadow of the Almighty" (Psalm 91:1). That protection had been total: he had outlived his enemies, outlived his rebellious children, outlived the wars that consumed lesser kings. But he could not outlive himself.
The Messiah — who descends from David — is introduced here precisely at the moment of David's physical decline. The promise does not end with the body. What David carried, what the covenant carried, passes forward. The rabbis were teaching that the vitality of the covenant is not biological. David grows cold. The fire moves on. It would warm the throne of his descendants for generations, and the rabbis believed it would warm the throne of the Messiah at the end of days. David's cold body is not the end of David's line. It is the sign that the line has gone somewhere else.