Luke 21:7

‘And they asked him, saying, “Teacher, when therefore will these things be? and what shall be the sign when these things are about to occur?” '

Revealing their typical Jewishness his hearers then asked when these things would be and what would be the signs that introduced their occurrence. In context they were asking about the destruction of the Temple and the casting down of its stones and gifts. Jesus' reply is quite vivid. The signs that signify its end will not be the political or natural events of great magnitude which are coming (Luke 21:8), nor will it be the tribulations that they themselves will have to face (Luke 21:12). The first sign of it will be when Jerusalem is being surrounded by armies (Luke 21:20), when it will be almost too late for anyone to do anything about it, although those who foresee it happening can flee (Luke 21:21), as the early Jerusalem church seems to have done. This should warn us too against seeking special signs of the second coming. The sign of that also is clear. The sign will be the glory that accompanies His arrival (Luke 21:27). So that will also be too late for anyone to do anything about. He will have come when least expected ‘like a thief in the night'.

‘Teacher.' This is a general standard method of addressing Jesus used by all types. It is an idea seen as applying to Him in connection with the Apostles (Luke 6:40); and is used by people of all kinds who approached Him (Luke 7:40; Luke 8:49; Luke 9:38; Luke 10:25; Luke 11:45; Luke 12:13; Luke 18:18; Luke 19:39; Luke 20:21; Luke 20:28; Luke 20:39; Luke 22:11). Luke's desire is to make the questioners anonymous so that all can apply it to themselves.