William Burkitt on Luke 21:29

In these words our Saviour declares the certainty of his coming to visit Jerusalem for all her barbarous and bloody cruelty towards himself, his prophets, and apostles; he is pleased to set forth this by the similitude of the fig-tree, whose beginning to bud declares the summer at hand; thus our Saviour tells them, that when they should see the fore-mentioned signs, they might conclude the destruction of their city and temple to be near at hand; and accordingly some of that generation, then living, did see these predictions fulfilled.

Learn, that God is no less punctual in the execution of his threatenings upon incorrigible sinners, than he is faithful in the performance of his promises towards his own people: the truth and veracity of God is as much concerned to execute his threatenings, as it is to fulfill his promises.