Komentaryo sa 2 Samuel 21:2: Rashi

And spoke to them. Words of appeasement [asking them] to put aside their feelings [of anger] and forgive Shaul and his household.

The Givonim were not part of the Bnei Yisroel. This is to say that they displayed how cruel they are, because they are not descendants of our forefather Avrohom. They have proven themselves unworthy to join with Yisroel and hence Dovid decreed that they not be permitted to marry into the Jewish community. He [Dovid] said, This nation [of Yisroel] has three characteristics, the people are merciful, they possess shame and perform kindful deeds for others. Whoever has these three characteristics is worthy of joining it [Yisroel].⁷They have shown themselves to be cruel and unmerciful and hence they do not deserve to join together with Yisroel. Yevomos 79a.

Sworn to them [that they would let them live]. During the days of Yehoshua when he made woodcutters and water drawers for the Altar.⁸Yehoshua 9:27.

In his zeal to avenge the Bnei Yisroel. Because he [Shaul] intended to clean and purify Yisroel and to take care of their [Yisroel's] needs, he wanted to kill them. This anger was for a good purpose as we find "Are you zealous for my sake?"⁹Bamidbar 11:29. And we also find "by the zeal for God's sake" as was said of Yeihuh.¹⁰See Melochim I, 19:10. This is the simple explanation of our verse. [But] according to the Midrashic intepretation, he [Shaul] only ordered that the kohanim be killed. And the zeal described here was not for a good purpose but rather for a bad purpose because he [Shaul] knew that his kingdom would not continue further from the day that he did not heed God's commandment concerning Amoleik,¹¹Shmuel I, 15:9. and from that time on, he was angry [and persecuted] them.