Matthew 10:27

That which I tell you, &c. We must not suppose that our Saviour was accustomed to deliver his instructions to his apostles in the secret of the night, or teach them in private by whispers. But here he uses a figure of speech, to convey to the minds of his apostles the insignificancy of Judea, where he was speaking in comparison of the whole world, which they were to instruct; and the low whisper of his voice, compared to the sound which they shall send forth to the ends of the earth. (St. John Chrysostom, hom. xxxv.) --- Upon the house-tops. the tops of the houses in Palestine were flat, and the inhabitants were accustomed to assemble on them and discourse together in great numbers. To preach, therefore, on the top of a house, is the same as to preach where there is a great concourse of people. (Menochius)