The Thirteen Attributes of Mercy
Exodus 34:6
God's self-description includes both 'rav chesed' (abundant in lovingkindness) and 'v'rachamim' (compassion), listing them as distinct divine qualities within the same revelation.
וַיַּעֲבֹ֨ר יְהֹוָ֥ה ׀ עַל־פָּנָיו֮ וַיִּקְרָא֒ יְהֹוָ֣ה ׀ יְהֹוָ֔ה אֵ֥ל רַח֖וּם וְחַנּ֑וּן אֶ֥רֶךְ אַפַּ֖יִם וְרַב־חֶ֥סֶד וֶאֱמֶֽת׃
The ETERNAL passed before him and proclaimed: “GOD! GOD! a Deity compassionate and gracious, slow to anger, abounding in kindness and faithfulness,
Why it matters — The juxtaposition of chesed and rachamim in the Thirteen Attributes is the classic biblical locus for exploring their difference.