What does Luke 12:2 mean?

Jesus continues applying His rejection of the example of the hypocritical Pharisees (Luke 12:1). At a dinner with Pharisees and their lawyers, Jesus condemned them for appearing holy while their hearts were like unmarked graves. They tithe on the smallest of herbs and love receiving honor in the synagogue, but they teach the people false doctrine, following the tradition of those who killed the Old Testament prophets (Luke 11:37–52).

Now, Jesus tells the disciples that the Pharisees' hidden sins will one day be made public. They will be judged for their secret plots (Luke 11:53–54). In fact, everyone's actions will be revealed in the final judgment, including the disciples' (1 Corinthians 4:5; Romans 2:16). The disciples might be enticed by the public approval the Pharisees receive, but they need to focus on Jesus, not the adoring crowds, even if such loyalty leads to their death (Luke 12:4–12).

The struggle is real. Much later, Peter will be faced with the choice between staying in the good graces of legalistic Jews-turned-Christ-followers or following Christ into unfettered community with Gentile Christians. Paul will chastise him when he chooses wrong (Galatians 2:11–14). It is not the extra-biblical regulations of the Pharisees that saves but God's grace, more specifically in Jesus' life, death, and resurrection, which we receive through faith in Christ (Ephesians 2:1–10).

Most likely, Jesus taught the same thing in different contexts. In Matthew's account, the phrases are a bit rearranged to show a different application: "So have no fear of them, for nothing is covered that will not be revealed, or hidden that will not be known" (Matthew 10:26). Matthew's account goes on to include the text in Luke 12:4–7 to show that the disciples should have courage to speak the truth, even if the Pharisees and other religious leaders threaten their lives. The disciples will follow Jesus' instructions in Acts 4—5.