Mat 10:23 But when they persecute you in this city, flee to another: for truly I tell you, You shall not have gone over the cities of Israel, until the Son of man comes.

The first part of this verse is not at all controversial.
"Persecute" is dioko, which means "to pursue," "to chase," or "to drive."
"Flee" is pheugo, which means "to flee," and "to take flight."

The second part is more interesting because it seems to be a prophesy that the apostles will not go to all the cities of Israel before Christ returns, possibly from the dead. However, the Greek doesn't say anything like that.

"Gone over" is teleo, which means "to complete," "to fulfill," and "to accomplish." It also means "to bring to perfection," "to pay what one owes," and "to execute a legal document."

"Be" is not the verb "to be" but the partical an, which means something that can occur under the right circumstances. It is usually translated as "whosoever" in the New Testament.

"Comes" is erchomai, which means "to start or set out," "to appear," or "to come or go." It has a wide variety of uses in ancient Greek showing all manner of movement. It does NOT mean return, for which Matthew uses another verb.

My suggestion for the second part of this verse: "You will not have brought the cities of Israel to perfection before the Son of Man comes into his own." On other words, Christ is telling the apostles not to worry about the fact that they are not going to convince everyone on this, their first experience with spreading the word. If we apply this to our own lives, it is a statement about the limitations on the scope of our human accomplisments during any single campaign.