There shall come forth a shoot from the stump of Jesse, and a branch from his roots shall bear fruit. And the Spirit of the LORD shall rest upon Him, the Spirit of wisdom and understanding, the Spirit of counsel and might, the Spirit of knowledge and the fear of the LORD.
Isaiah calls [Christ] a "Shoot" (Isaiah 11:1) and says that He sprouts forth like an outstanding and excellent young plant (Isaiah 53:2). With this expression Isaiah indicates that Christ's kingdom is always growing. You see, the Spirit and Christ's Word are always in a state of growing. They move forward constantly, and as a consequence they bear greater fruit. The world sets itself against it with might and main to cause this branch to wither and dry. It attacks the branch with death, disgrace, poverty, and every evil. God, however, always causes it to grow. He supplies it with enough moisture so that it still grows and flourishes even in the burning summer sun.
From Lectures on Zechariah (Latin text) (Luther's Works 20:40)