The corresponding letter to this chapter is Shin – Divine power; provision; protection.
Chapters 21 thru 24 are an epilogue and are not necessarily in chronological order.
Sh'mu'el Bet 21:1-7 Now there was a famine in the days of David for three years, year after year; and David sought the presence of the L-RD. And the L-RD said, "It is for Sha’ul and his bloody house, because he put the Giv’onim to death." So the king called the Giv’onim and spoke to them (now the Giv’onim were not of the sons of Israel but of the remnant of the Emori, and the sons of Israel made a covenant with them, but Sha’ul had sought to kill them in his zeal for the sons of Israel and Y’hudah). Thus David said to the Giv’onim, "What should I do for you? And how can I make atonement that you may bless the inheritance of the L-RD?" Then the Giv’onim said to him, "We have no concern of silver or gold with Sha’ul or his house, nor is it for us to put any man to death in Israel." And he said, "I will do for you whatever you say." So they said to the king, "The man who consumed us, and who planned to exterminate us from remaining within any border of Israel, 6 let seven men from his sons be given to us, and we will hang them before the L-RD in Giv’ah of Sha’ul, the chosen of the L-RD. "And the king said," I will give them." But the king spared M’fivoshet, the son of Y’honatan the son of Sha’ul, because of the oath of the L-RD that was between them, between David and Sha’ul's son Y’honatan.
David recognized that the famine must be judgment from G-d and went to Him to see if there was something that Israel could do to change the situation.
Here we see divine protection for M’fivoshet.
Sh'mu'el Bet 21:8-9 So the king took the two sons of Ritzpah the daughter of Ayah, Armoni and M’fivoshet whom she had born to Sha’ul, and the five sons of Merab the daughter of Sha’ul, whom she had born to Adriel the son of Barzillai the Mecholati. Then he gave them into the hands of the Giv’onim, and they hanged them in the mountain before the L-RD, so that the seven of them fell together; and they were put to death in the first days of harvest at the beginning of barley harvest.
Merab, some translations say Mikhal. Mikhal was David’s first wife and she was childless. It appears that she adopted and raised these 5 sons of Adriel and Merab.
So 7 male descendants of Sha’ul were handed over to be put to death to settle the score.
Sh'mu'el Bet 21:10-14 And Ritzpah the daughter of Ayah took sackcloth and spread it for herself on the rock, from the beginning of harvest until it rained on them from the sky; and she allowed neither the birds of the sky to rest on them by day nor the beasts of the field by night. When it was told David what Ritzpah the daughter of Ayah, the concubine of Sha’ul, had done, then David went and took the bones of Sha’ul and the bones of Y’honatan his son from the men of Yavesh-Gil’ad, who had stolen them from the open square of Beit-Sh’an, where the P’lishtim had hanged them on the day the P’lishtim struck down Sha’ul in Gilboa. And he brought up the bones of Sha’ul and the bones of Y’honatan his son from there, and they gathered the bones of those who had been hanged. And they buried the bones of Sha’ul and Y’honatan his son in the country of Binyamin in Tzela, in the grave of Kish his father; thus they did all that the king commanded, and after that G-d was moved by entreaty for the land.
G-d again provides. G-d also protects David from harm from evil giant men.
Sh'mu'el Bet 21:15-22 Now when the P’lishtim were at war again with Israel, David went down and his servants with him; and as they fought against the P’lishtim, David became weary. Then YIishbi-B’nov, who was among the descendants of the giant, the weight of whose spear was three hundred shekels of bronze in weight, was girded with a new sword, and he intended to kill David. But Avishai the son of Tz’ruyah helped him, and struck the P’lishti and killed him. Then the men of David swore to him, saying, "You shall not go out again with us to battle, that you may not extinguish the lamp of Israel." Now it came about after this that there was war again with the P’lishtim at Gov; then Sibkhai the Hushati struck down Saf, who was among the descendants of the giant. And there was war with the P’lishtim again at Gov, and Elchanan the son of Ya’arei-Orgim the Beit-Lachmi killed Golyat the Gitti, the shaft of whose spear was like a weaver's beam. And there was war at Gat again, where there was a man of great stature who had six fingers on each hand and six toes on each foot, twenty-four in number; and he also had been born to the giant. And when he defied Israel, Y’honatan the son of Shim’ah, David's brother, struck him down. These four were born to the giant in Gat, and they fell by the hand of David and by the hand of his servants.
Elchanan the son of Ya’arei-Orgim the Beit-Lachmi killed Golyat - This is a bit puzzling because we all know that David killed Golyat. So there are a couple of possibilities. One is that Elchanan is amother name for David and the other one is that there was a scribal error and it should read “Elchanan the son of Ya’arei-Orgim the Beit-Lachmi killed the brother of Golyat”