John Lightfoot on Luke 12:3

[That which ye have spoken in the ear.] I have elsewhere spoken of a doctor whispering in the ear of his interpreter. The reason of this usage is given us in Chagigah, because the law is delivered silently; and the reason of this is, it is delivered silently, because of Satan.

However, these words are not to be understood of any such kind of whispering into the ears of the interpreter, but concerning any matter that may have been spoken in never so much secrecy and design not to have been known again. The doctor whispered into the ear of the interpreter to that end, that his disciples might publish what he had said. But here is meant, whatever any had the greatest purpose to conceal, yet God will reveal it; not much unlike that passage in Ecclesiastes 10:20. Our Saviour intimates the folly as well as the wickedness of dissimulation, because in time the visor shall be taken off, and the most dissembled hypocrisy exposed to naked view.