This generation
(Greek, "genea", the primary definition of which is, "race, kind, family, stock, breed"). (So all lexicons.) That the word is used in this sense because none of "these things," that is, the world-wide preaching of the kingdom, the great tribulation, the return of the Lord in visible glory, and the regathering of the elect, occurred at the destruction of Jerusalem by Titus, A.D. 70. The promise is, therefore, that the generation -- nation, or family of Israel -- will be preserved unto "these things"; a promise wonderfully fulfilled to this day.