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 that Israel are performers of kindness? As it is written, “Hashem your God will keep for you the covenant and the 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.