Jamieson, Fausset and Brown on Matthew 12:36

36. But I say unto you, That every idle word that men shall speak, they shall give account thereof in the day of judgment--They might say, "It was nothing: we meant no evil; we merely threw out a supposition, as one way of accounting for the miracle we witnessed; if it will not stand, let it go; why make so much of it, and bear down with such severity for it?" Jesus replies, "It was not nothing, and at the great day will not be treated as nothing: Words, as the index of the heart, however idle they may seem, will be taken account of, whether good or bad, in estimating character in the day of judgment."

Mt 12:38-50. A Sign Demanded and the Reply--His Mother and Brethren Seek to Speak with Him, and the Answer. ( = Lu 11:16, 24-36; Mr 3:31-35; Lu 8:19-21).

A Sign Demanded, and the Reply (Mt 12:38-45).

The occasion of this section was manifestly the same with that of the preceding.