The basis for confidence in the face of persecution is an understanding that whatever is presently hidden will eventually come out into the open. This proverbial statement applies to the truth about Jesus that the fearful disciple might seek to keep hidden for fear of opposition. It also applies to the disciple himself who might want to hide instead of letting his light shine. It applies also to the preceding teaching about persecution. [source][source][source]
What Jesus told His disciples privately would eventually become public knowledge, so they should declare it publicly. In Palestine common flat-roofed houses were good places from which to make public addresses. [source][source][source]
"Good news is not meant to be kept under wraps, however little some people may wish to hear it." [1][source]