That verse forms a transition to the section containing the illustrative parable and the reiteration of the assurance that Christ's words would certainly be fulfilled. The disciples might naturally quake at the prospect, and wonder how they could face the reality.
Jesus gives them strong words of cheer, which apply to all dreaded contingencies and to all social convulsions. What is a messenger of destruction to Christless men and institutions is a harbinger of full redemption' to His servants. Earthquakes but open their prison doors and loose their bands, they should not shake their hearts.
Historically the fall of Jerusalem was a powerful factor in the deliverance of the Church from Jewish swaddling-bands which hampered its growing limbs. For all Christians the destruction of what can perish brings fuller vision and possession of what cannot be shaken. To Christ's friends, all things work for good. So the parable which at first sight seems strangely incongruous becomes blessedly significant and fitting. The gladsome blossoming of the trees, the herald of the glories of summer, is a strange emblem of such a tragedy, and summer itself is a still stranger one of that solemn last judgment. But the might of humble trust in Him who comes to judge makes His coming summer-like in the light and warmth with which it floods the soul, and the rich fruitage which it produces there.
Observe, too, that the parable confirms the idea of a process having stages, for the lesson of the blossoming fig-tree is not that summer has come, but that it is nigh.
The solemn assurance in Luke 21:32, made more weighty by the Verily I say,' seems at first sight to bring the final judgment within the lifetime of the generation of the hearers. But it is noteworthy that the expression till all things are fulfilled' is almost verbally identical with that in Luke 21:22, which refers only to the destruction of Jerusalem, and is therefore most naturally interpreted as having the same restricted application here. The difference between the two phrases is significant, since in the former the certainty of fulfilment is deduced from the fact of the things' being written--that is, they must be accomplished because they have been foretold in Scripture,--whereas in the latter Christ rests the certainty of fulfilment on His own word. That majestic assurance in Luke 21:33 comes well from His lips, and makes claim that His word shah outlast the whole present material order, and be fulfilled in every detail. Think of a mere man saying that!
