NOTES for Zec 13:9
The prophets said many time that they will meet the Messiah promised by God and that not all the people will enter the messianic Kingdom, but the remnant, which by definition consists not of the majority, but of the minority of people. Zechariah speaks in that case about a third of the population. Probably, it is necessary to consider this number symbolical : because, the Jewish community of Babylon that survived the captivity, and whose members could be considered as the remnant of which the prophets spoke about, was much less than a third of the population of the Jewish people before captivity.
But now all prophets say the same thing about the meaning of what happened. Zechariah and here recourses to symbols: he speaks about the "purifying fire", about “the melting" of people. It is particularly remarkable that all this is already said in the period before captivity. As we see, it was revealed to the prophet that before the arrival of the Messiah the people wait another for trial, similar to the one he experienced during the Babylonian invasion.
Such trial could be historically considered the persecutions of Antiochus Epiphanes and the following answer to them the Maccabees wars. Of course, talking about the destruction of a third of the people during the persecutions is not necessary in this case, but, as we see, it was all about that proportion, which is characteristic of the corresponding technological process mentioned by the prophet, whose impurities contained in the ore is separated from metal.
The meaning of the prediction is completely clear: in order to enter the Kingdom, it is necessary to get rid of everything that is incompatible with its life. And during the persecutions, the superficial in man, as in any critical situation, separates itself from the main which is its spiritual essence. And the people in general are divided into those who are ready to walk by the way of the Kingdom, in spite of the persecutions, and those who are not ready for the trials. Control is rigid, but inevitable.