Jeremiah 17:5 - Ellicott's Commentary On The Whole Bible

Cursed be the man... — The words are vehement and abrupt, but they burst from the prophet’s lips as proclaiming the root evil that had eaten into the life of his people. Their trust in an arm of flesh had led them to Egyptian and Assyrian alliances, and these to “departing from the Lord.” The anathema has its counterpart in the beatitude of Jeremiah 17:7. The opening words, Thus saith the Lord, indicate, perhaps, a pause, followed as by a new message, which the prophet feels bound to deliver. It is significant that the prophet uses two words for the English “man.” the first implying strength, and the second weakness.