Matthew 10:27 - Ellicott's Commentary On The Whole Bible

What I tell you in darkness. — The words point to our Lord’s method of teaching, as well as to the fact of its being esoteric, and disclosed only to the chosen few, and to them only as they were “able to bear it” (John 16:12). Parables, and dark sayings, and whispered hints, and many-sided proverbs, were among the forms by which He led them on to truth. They, in their work as teachers, were not to shrink through any fear of man from giving publicity to what they had thus learnt. To “proclaim on the housetops” — the flat roofs of which were often actually used by criers and heralds for their announcements — is, of course, a natural figure for the fullest boldness and freedom in their preaching.