At that time, Jesus said to His disciples: When they shall persecute you in this city, flee into another. Amen, I say to you, you shall not finish all the cities of Israel till the Son of man come. The disciple is not above the master, nor the servant above his lord. It is enough for the disciple that he be as his master, and the servant as his lord. If they have called the good of the house Beelzebub, how much more them of his household? Therefore fear them not; for nothing is covered that shall not be revealed; nor hid that shall not be known. That which I tell you in the dark, speak ye in the light; and that which you hear in the ear, preach ye upon the housetops. And fear ye not them that kill the body, and are not able to kill the soul; but rather fear Him, that can destroy both soul and body into hell.
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Note: by the way, I was shocked that someone I know who actually teaches Sunday school thought that "Him" refers to Satan, that Jesus is saying to fear Satan! Oh my God, are people totally unable to read? "Him" refers to God. Only God can destroy the body and soul by sending someone into hell. Satan can't destroy souls dummies. And Satan does not send people to hell. So Jesus is reminding people to not fear other people who can only kill the body, but to rather have healthy fear of God who can destroy not only the body but also the soul by sending the persons to hell.
People have no reason to fear Satan, and Jesus would never preach that and was in fact the walking and talking role model of how Satan is not to be feared. All Satan does is tempt, that is all. Satan does not do bad things to people; people do bad things to each other. Satan is the example where "just say no" really works. If Satan has no power to tempt a person then Satan virtually disappears out of a person's life. He's just not even around. Like I've pointed out, it's not like Satan was running around kicking sand in the faces of baby dinosaurs before humans were around. Satan exists only in the form of temptation and deception. He has no power over human bodies or souls and he certainly has no power to judge their fate.
So in this very valuable exhortation and teaching by Jesus, while he is focusing on bolstering the disciples' courage to speak the truth and declare the faith even if their lives are threatened, he is also reminding them that only One, who is God, can go past destroying the body and also destroy the immortal soul, should God have to send that person to hell where such is achieved.
Fear of God means fearing to lose your relationship to God. It's not fear of God like God is waiting around each corner to do something bad to you. (That's a talent of humans, unfortunately). God waits around each corner to love each person and to be loved. Fear of God is not terror, but the fear of losing one's relationship with God so that one may indeed lose not only body but also soul for eternity.
OK, while I'm at it I ought to be sure I've walked you through the right way to interpret this whole passage. First of all Jesus is encouraging the disciples to not be afraid of those who oppose their preaching, even if the opponents threaten them with their lives. Next he is telling them to keep it all in context, that they are not going to convert the whole world. This is what Jesus means when he says they won't get to all of Israel before the Son of man comes. Remember that Jesus was only preaching to Jews when he lived. So Israel means the world in this context, not just the "state" of Israel. So Jesus was saying that just as he would not get to convert all of Israel, the disciples should not assume that they will either. All of "Israel" will only be converted when the Son of man comes (the Second Coming at the End of Days/Time and Final Judgment). So Jesus is basically tell them to be realistic in their aspirations to evangelize and convert.
This is why Jesus goes into a whole section about humility. This is an important concept because he is distinguishing between being a good role model and being "better" than someone. Jesus is saying that if he himself cannot convert everyone then how can they think that they can convert everyone? The followers are not better than or more talented or gifted than the master. So Jesus is cautioning them not to start to think that they are better than him or can achieve "more." However, he then tells them that followers should emulate and try to be like their master. This is why he says "It is enough for the disciple that he be as his master, and the servant as his lord." You see? Jesus is teaching the disciples to emulate him but not to assume that they can do what he could not (specifically convert all of Israel).
He then goes on to repeat a common slander that was made against Jesus by his detractors and those who opposed his teaching. Jews who opposed Jesus often accused him of being Beelzebub, which is the devil. So Jesus is basically saying, somewhat wryly, that if these opponents are crazy enough to call Jesus the devil, imagine how crazy they will be to you, his followers. So he is repeating his advice which is that if people are crazy enough to think that Jesus is the devil, then they will think that of the disciples too, and to not fear them, but not to bother with them after the initial attempt to evangelize and convert.
Jesus then builds on this advice about the slander by pointing out that the truth will always come out. People who accuse Jesus and his followers of being Beelzebub, etc, will learn the truth at some point or another (though it might be when they die and get the unpleasant surprise then). So Jesus is reassuring them that even if they are accused of dreadful and false things, do not despair, because the truth will come out.
Jesus then exhorts them to not just wait for the truth to come out but always to highlight and amplify the truth at all times. So what they have learned from Jesus, for example, they should take and broadcast as much as they can. This is, by the way, another scriptural reference that refutes that Jesus "had secrets" or taught the disciples secret lore that only New Age geniuses can detect in the future through secret lemonade writing or something. Jesus continually tells the disciples to repeat to everyone all that he, Jesus, had taught them.
Then he goes into the reminder to not fear those who can kill the body, but fear losing one's body and soul by losing God and ending up in hell, as I detailed already above.
I hope this helps. This is crucial teaching by Jesus in his very words and should be well understood in factual analysis by all Christians and people of faith.