What does 2 Samuel 18:20 mean?

They took Absalom and cast him into the great pit in the forest, and raised over him a very great heap of stones. Then all Israel fled, each to his own tent.

Now Absalom in his lifetime had taken and reared up for himself the pillar which is in the king’s valley, for he said, “I have no son to keep my name in memory.” He called the pillar after his own name. It is called Absalom’s monument, to this day.

Then Ahimaaz the son of Zadok said, “Let me now run, and carry the king news, how Yahweh has avenged him of his enemies.”

Then Joab said to the Cushite, “Go, tell the king what you have seen!” The Cushite bowed himself to Joab, and ran.

Then Ahimaaz the son of Zadok said yet again to Joab, “But come what may, please let me also run after the Cushite.” Joab said, “Why do you want to run, my son, since that you will have no reward for the news?”

“But come what may,” he said, “I will run.” He said to him, “Run!” Then Ahimaaz ran by the way of the Plain, and outran the Cushite.