Albert Barnes Commentary 2 Samuel 18:19

"Then said Ahimaaz the son of Zadok, Let me now run, and bear the king tidings, how that Jehovah hath avenged him of his enemies." — 2 Samuel 18:19 (ASV)

Ahimaaz was a well-known runner (2 Samuel 18:27). In those simpler times, speed was a heroic virtue (compare 2 Samuel 2:18). During Hezekiah’s reign, we find an established system of postal runners (2 Chronicles 30:6, 10). The same name, “runners,” is used for the Persian posts in Esther 3:13, even though at that time they rode on mules and camels.

Bear tidings - The original word is used almost exclusively for bearing good tidings and is therefore rendered in the Septuagint (though not always) as εὐαγγίζεσθαι euangelizesthai (2 Samuel 4:10; 1 Samuel 31:9). In 2 Samuel 18:21, the command is not to “carry the good tidings,” but simply to “tell” or “announce.”