This verse concludes a passage describing several battles fought between David's forces and the Philistines. Specifically, it refers to four Philistine warriors who were descendants of a giant from the city of Gath. Here's a breakdown of what it means:

"These four were born to the giant in Gath": This identifies the four individuals as offspring of a giant (likely a particularly tall or powerful warrior) who lived in Gath, a major Philistine city. Gath was famous for its giants, including Goliath.

"and they fell by the hand of David, and by the hand of his servants.": This states that these four giants were defeated and killed. The verse clarifies that their deaths were due to the actions of David himself and his loyal soldiers (his servants or men). This suggests that David might have personally killed one or more of them, while his soldiers accounted for the rest. It highlights that the victories were a result of both David's leadership and the bravery of his men.

In essence, the verse serves to emphasize a few key points:

The ongoing conflict: It underscores the continuing struggles between Israel (led by David) and the Philistines.
The strength of the enemy: It acknowledges that the Philistines had formidable warriors, descendants of giants, who posed a serious threat.
David's power and leadership: It demonstrates David's strength and courage in personally engaging in battle and defeating these giants, as well as the effectiveness of his army under his command.
Divine favor: Implied within the victory is the idea that God was with David and his army, enabling them to overcome even seemingly insurmountable foes.

The verse functions as a summary of a series of encounters with giant-like Philistine warriors, reinforcing the narrative of David's military prowess and the establishment of his kingdom.