Adam Clarke on Zechariah 11:1

Open thy doors, O Lebanon - I will give Mr. Joseph Mede's note upon this verse: - "That which moveth me more than the rest, is in chap. 11, which contains a prophecy of the destruction of Jerusalem, and a description of the wickedness of the inhabitants, for which God would give them to the sword, and have no more pity upon them. It is expounded of the destruction by Titus; but methinks such a prophecy was nothing seasonable for Zachary's time, (when the city yet for a great part lay in her ruins, and the temple had not yet recovered hers), nor agreeable to the scope. Zachary's commission, who, together with his colleague Haggai, was sent to encourage the people, lately returned from captivity, to build their temple, and to instaurate their commonwealth. Was this a fit time to foretell the destruction of both, while they were yet but a-building? And by Zachary too, who was to encourage them? Would not this better befit the desolation by Nebuchadnezzar?" I really think so. See Mr. J. Mede's 61. Epistle.

Lebanon signifies the temple, because built of materials principally brought from that place.