As a youth, nineteen years of age or younger, David fought and killed the giant Goliath. We know this about David’s age because he was the youngest of eight brothers and at the time his three eldest brothers were fighting in Saul’s army but he wasn’t (1 Samuel 17:13&14) and the age one had to be to fight in the army was 20 years old or more ( Numbers 1:3).
In 1 Chronicles 20, David was now king of Israel and 3 men who were connected with him in some way, killed giants or their offspring or relatives. In verse 4 Sibbechai, one of David’s mighty men (1 Chronicles 11:29) killed a giant’s (thought to be Goliath) son. In verse 5 Elhanan a warrior in David’s time referred to as one of his servants (verse 8) killed Goliath’s brother, and in verse 7 Jonathan David’s nephew killed a giant ( “a man of great stature”) that had 24 fingers and toes !
All three of these men were associated with David in some way and therefore were under his influence, and the fact David had killed a giant was part of that influence and I’d suggest a factor that led them to kill giants and those connected with them. There is no influence like example. It might be said, we influence best in 3 ways….example, example and example. This seems to have held true in the case of David the giant slayer.
Never underestimate the power of influence by example.