"When they persecute you in this city, flee to another. For assuredly, I say to you, you will not have gone through the cities of Israel before the Son of Man comes. A disciple is not above His teacher, nor a servant above his master. It is enough for a disciple that he be like his teacher, and a servant like his master. If they have called the master of the house Beelzebub, how much more will they call those of his household! Therefore do not fear them. For there is nothing covered that will not be revealed, and hidden that will not be known. Whatever I tell you in the dark, speak in the light; and what you hear in the ear, preach on the housetops."
When the apostles faced persecution, they were not to throw their lives away. Rather, they were to flee from one city to the next and go to where they could do the most good in further service to the Lord. After the church was established, the fleeing of Christians from city to city was a significant factor in spreading the gospel (cf. Acts 8:1ff).
There are many different interpretations of Jesus' statement in Matthew 10:23 - "You will not have gone through the cities of Israel before the Son of Man comes." I believe, however, that Colossians 1:23 limits the possible interpretations to something that happened in the first century. The simplest interpretation is that the disciples would not be able to get all of their work done before Jesus would physically come after them to these towns. The other possibility is that the phrase "before the Son of Man comes" refers to the establishment of the church (cf. Matt. 16:28; Mark 9:1; Acts 2).
In Matthew 10:24,25, Jesus warned His apostles that they should not expect better treatment than He received. When one suffers the humiliation and rejection that comes from being faithful, he should rejoice in the opportunity to be treated as Jesus was (cf. John 15:20,21; Acts 5:41). When he feels like complaining about the abuse, he ought to think: "Who am I to complain of suffering, when my Lord and Master suffered so much more than this for me?"
Jesus offered further motivation for spiritual endurance in Matthew 10:26. It is sometimes the case that disciples will suffer from injustice that is so covered up from the eyes of the world that it appears like justice, and there is nothing more disheartening than this. However, Jesus gives His assurance that nothing will remain hidden or covered forever (cf. Eccl. 12:13,14). Thus, there is no reason to be afraid of earthly injustice, for God knows the truth and will expose it in the end.
"Whatever I tell you in the dark, speak in the light; and what you hear in the ear, preach on the housetops" (Matt. 10:27). Jesus urged them to faithfully reveal all of the truth that would be given to them. They should be able to shout it out loud and clear without fear.