Because the matan Torah (giving of the Torah) was graciously bestowed through Moshe [Rabbeinu] [DEVARIM 32:46 SHEMOT 31:18; 34:28], but Chesed and Emes of Hashem came through [Rebbe,] Melech HaMoshiach Yehoshua [Ex 34:6; Ps 25:10; 40:11; 85:11; Yochanan 1:49].