He referencing his Passion and coming into His Kingdom. He instructs them to flee (whenever possible) from persecution, because he did not want them to put themselves in harms way since they may end up longing for the crown of martyrdom, but being of weak mind and flesh, they might not have been able to bear and endure it. He instructs them to flee, but their flight is restricted to Judea for now, and it is a temporary instruction (until He comes into His Kingdom).
The last half of Matthew 10:23 “may be interpreted in two ways: (a) you will not have converted all of Israel before the Second Coming of Christ; (b) you will not have preached the gospel in all the towns of Palestine before the destruction of Jerusalem, which is a type of the end of the world.” (A Commentary on the New Testament, prepared by the Catholic Biblical Association, 1942, page 80.)
I agree with this reading. Combined with other passages it shows how the authors of the New Testament believed that Jesus’ return would happen within their lifetimes.
The problem with this interpetation is that the “you” referred to in the passage (the 12 apostles) are all dead. The passage clearly suggests that the apostles would still have at least one more town to flee to when Christ makes his second coming. Instead this is saying that they will all pass away and Christ will return at some point afterward. Reading the passage it stresses the quickness of his return and suggests that at least one of the apostles be alive upon his second coming. This first understanding completely (and I believe incorrectly) undercuts this point.
(b) you will not have preached the gospel in all the towns of Palestine before the destruction of Jerusalem, which is a type of the end of the world." (A Commentary on the New Testament, prepared by the Catholic Biblical Association, 1942, page 80.)
That’s the kind of reading where one is forced to ignore the plain meaning of what was originally written, and then twisting the meaning of words to get an interpretation that reaches a conclusion one finds satisfactory (e.g. that Jerusalem’s destruction is equal to Jesus’ second coming). This 2nd reading too undercuts the swiftness by downplaying the major point of the passage (that the apostles will run out of towns to flee to before his return) and totally reconfigures it as one that tries to make it seem the point is that the apostles will all be dead before Jesus returns.
Here are earlier verses for context. We’re the apostles persecuted this badly?
21*“Brother will betray brother to death, and a father his child; children will rebel against their parents*and have them put to death.22You will be hated by everyone because of me,*but the one who stands firm to the end will be saved.23When you are persecuted in one place, flee to another. Truly I tell you, you will not finish going through the towns of Israel before the Son of Man comes.
Ver. 23. Flee into another. Tertullian, with some others, held it never lawful to fly in the time of persecutions, against both the doctrine and example of our Saviour, Christ. — You shall not finish, &c. St. Chrysostom thinks the sense of these words is, you shall not go through, and have finished your preaching in all the cities of Israel, till I, who follow you, shall come, and join you again. Others expound it, till the coming of me, your Messias, shall be published, and owned after my resurrection. (Witham)