Blessed are those who are persecuted for the sake of righteousness, for theirs is the kingdom of the heavens.
Many saints who have done their best to be righteous have suffered persecution as a result. In their environment, business, or employment there were many unrighteous things. Because they desired to be righteous in that situation, they suffered persecution from others.
This verse says that those who are persecuted for righteousness are blessed, “for theirs is the kingdom of the heavens.” If we seek righteousness at a cost, the kingdom of the heavens becomes ours: we are in its reality now, and we shall be rewarded with its manifestation in the coming age.