What is the importance of faithfulness that makes it a weighty provision of the law?  See Deut 32:20, 1Sa 26:23, Hos 2:20, Hab 2:4 and consider again the New Testament relationship of mercy to the Old Testament concept of chesed that is the foremost responsibility of a covenant relationship, a key responsibility for which we understand to include faithfulness.  Consider also that the word is used throughout the LXX for the Hebrew emunah that is also commonly translated as truth; see Pro 3:3, 12:17,22 (in both NAS and KJV), Pro 16:6, Jer 5:1,3, 7:28, 9:3, and Jer 15:18 where the word is negated to mean an intermittent stream or wadi that is unreliable and cannot be counted upon.

Notice in Mat 23:23 that the KJV translates the same word as faith, as it is normally translated throughout the New Testament; see for example Rom 1:17, Gal 2:16, Eph 2:8-9, 2Ti 2:22, Heb 6:1, 10:38-11:1.  See also Rom 4:16 and consider the faith of Abraham that was reckoned to Him as righteousness in Gen 15:6, the conviction he had that God’s promise, though unseen, was true and would come to pass, so that his conviction manifested itself in the faithfulness God spoke of in Gen 18:19; see Rom 4:19-24.  What does this teach us about the nature of true saving faith: is it just a belief that gives intellectual assent, or is it a conviction that manifests itself in a life-altering faithfulness to that conviction?  How does this help us understand the justification by faith that is apart from the works of the Law spoken of by Paul, and the relation of that faith to works of righteousness?  See Rom 3:21-31, Jam 2:14-26, and Gal 5:22 where the same word for faith is again translated as faithfulness.

Why is it that these three—justice, mercy, and faithfulness—are described as the weightier provisions of the law?  I.e., what is it that gives them their weight?  See Psa 25:9-10, 33:4-5, 89:14, 100:5-101:1, Isa 16:5, Hos 2:19-20.  What does this teach us about the three most important qualities for understanding the nature and character of God?  “God is love” (1Jo 4:8,16); what does this teach us about the three most important aspects of love?  What do these things then teach us about the three most important characteristics of those who would enter into God’s kingdom?