Thou shalt bear no tidings. — Ahimaaz appears to have been in favour both with David (comp. 2 Samuel 18:27) and with Joab. Joab, therefore, well knowing how painful to David would be the news of the death of Absalom, refused to let Ahimaaz bear it. The word is used, with rare exceptions, of good tidings.
Related Commentaries of 2 Samuel 18:20
2 Samuel 18:20
20 And Joab said unto him, Thou shalt not bear tidings this day, but thou shalt bear tidings another day: but this day thou shalt bear no tidings, because the king's son is dead.