The kind of persecution which produces the “kingdom of Heaven” is martyrdom. Originally the word “martyr” meant “witness” (the Greek word for martyr is μάρτυς, witness), but so many of the early Christian witnesses were killed that it came to have the modern meaning of “one who dies for their faith.” Martyrs were seen in John’s vision below the altar of God (see Revelation 2:11). This means they were holy because of their sacrifice, the Heavenly altar being a symbol of them having shed their blood as witnesses. Joseph Smith and Hyrum joined those who qualified for such a witness. Blessed are those who are willing to endure persecution for His name’s sake. For they are those who are willing to develop faith which cannot be obtained in any other way. It is through the sacrifice of all things that faith necessary for salvation is developed.1See also PERSECUTION.
1 “3 Nephi 12:10,” Oct. 7, 2010, blog post.