Parashas Eikev · Passuk 7:12
And if you do obey these rules and observe them carefully, the ETERNAL your God will maintain faithfully for you the covenant made on oath with your fathers:
Torah Temimah points to Yerushalmi Kiddushin 1:1.
TT lemma: ואת החסד.
Sefaria — Yerushalmi Kiddushin 1:1
English: It was taught: The Holy One gave Israel three good gifts — they are merciful, bashful, and performers of kindness. Whence “performers of kindness”? From “Hashem your God will keep for you the covenant and the kindness.” One who has the opposite traits — brazenness, cruelty, hatred of people, and no kindness — is strongly suspected of not belonging to a fit Israelite family. By this sign David excluded the Gibeonites from entering the community of Israel: they were brazen, would not be appeased, showed no mercy to Saul’s house, and did not repay Israel’s earlier kindness.
Custom (Yerushalmi — defining traits of Israel)
Kindness is a defining mark of Israel. Its opposite raises a serious doubt of lineage; David applied this criterion to the Gibeonites.