What does Luke 11:48 mean?

Jesus is taking His time to thoroughly explain how the lawyers of the Pharisees are complicit in the murders of God's prophets hundreds of years prior. The lawyers interpret and enforce an extra-biblical Oral Law which scribes added to the Mosaic law. God designed the Mosaic law to be simple to follow, so long as the Jews trusted Him. The Oral Law, however, is virtually impossible to keep but easy for the Pharisees to twist to their advantage.

"Them," the people killed, are God's prophets of the Old Testament. The "fathers" are the scribes of the intertestamental period: those who lived between Malachi and Jesus and who developed the Oral Law. These scribes "killed" the prophets by teaching that their words from God were incorrect and insufficient. For instance, it was not enough to teach the people to refrain from work on the Sabbath; the scribes added dozens of specific ways in which "work" could be interpreted. Such lessons taught the people they had to work for God's salvation, hindering them from entering the kingdom of God (Luke 11:52).

The religious leaders, whom the lawyers represent, also killed the prophets literally. Zechariah was murdered for confronting king Joash's idolatry (2 Chronicles 24:20–22). According to historical tradition, Jeremiah was put to death in Egypt after insisting God wanted Israel to submit to Babylon.

The "tombs" may be the final resting place of the prophets Haggai, Zechariah, and Malachi on the Mount of Olives in a cave system called the "Tombs of the Prophets." "Sepulchre," from the King James Version, is an older word for "tomb," especially one in a cave.

Jesus will remind His disciples of the lawyers' hypocrisy in Matthew 23:29–36.