One who loves G-d does not need to be instructed to do so. By contrast one who does not love G-d telling one to do so won’t change their mind.
“Moses then told the Jewish people that the proper response to G‑d’s self-revelation through the Torah is to fulfill His commandments out of love.
If someone loves G‑d, he does not need to be told to do so; if he does not love G‑d, telling him to will not change his mind. Therefore, both the medieval sage Rabbi Moses Maimonides and the founder of Chasidism, Rabbi Yisrael Ba’al Shem Tov, explain this verse to be both a commandment and a promise. We are commanded to contemplate the unity of G‑d, which is described in the preceding verse – ”Hear, O Israel, G‑d is our G‑d, G‑d is one.” If we meditate on the meaning of this verse deeply enough, we are assured that will we indeed thereby come to love G‑d.1Derech Mitzvotecha 199b