וַיֹּ֙אמֶר֙ לְכָ֣ה אִתִּ֔י וּרְאֵ֖ה בְּקִנְאָתִ֣י לַיהוָ֑ה וַיַּרְכִּ֥בוּ אֹת֖וֹ בְּרִכְבּֽוֹ׃
Poczem rzekł do niego: Pójdź zemną, a zobacz żarliwość moją dla Wiekuistego; i tak wsadzono go do powozu jego.
Rashi
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.