Albert Barnes Commentary Isaiah 37:6

"And Isaiah said unto them, Thus shall ye say to your master, Thus saith Jehovah, Be not afraid of the words that thou hast heard, wherewith the servants of the king of Assyria have blasphemed me." — Isaiah 37:6 (ASV)

With which the servants ... - Hebrew, נערי na‛ărēy - The ‘youth,’ or the young men. The word properly denotes boys, youths, young men; and is used here probably by way of disparagement, in contrast to an embassy that would be truly respectable, made up of aged men.

Have blasphemed me - God regarded these words as spoken against himself, and he would vindicate his own honor and name.