,תרי״ג מצות ניתנו לישראל, בא חבקוק והעמידן על אחת
.שנאמר: וצדיק באמונתו יחיה. – מכות כד
This means, it is as if all the mitzvot consisted of this one mitzvah of Emuna alone, for through Emuna alone one will come to fulfill all the 613 mitzvot.
Because, when his heart will rejoice and be glad with his faith in Hashem’s unity, in perfect joy, as though he were obligated by just this one mitzvah, and it alone were the purpose for which he and all the worlds were created, by the power and vitality of his soul generated from this great joy, his soul will soar far above all obstacles hindering his fulfillment of all the 613 mitzvot; both from within, and from without.
(Lessons in Tanya Chapter 33)