Will Not Finish Before

Matthew 10:21-23 NIV
“Brother will betray brother to death, and a father his child; children will rebel against their parents and have them put to death. 22 You will be hated by everyone because of me, but the one who stands firm to the end will be saved. 23 When 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.

Jesus was speaking to His disciples about witnessing to Israel. He is sending them out on a mission which stretches into the end of the age. The task will not be complete before the Son of Man returns. The time of the Gentiles will come to an end, and a remnant of Israel will be saved. Persecution and hardship have been bourn by this people who rebelled against God. Instead of being the first people to receive grace and share it with the world, they will instead receive grace at the last.
The first shall be last, and the last will be first, but we will all stand in that same grace.