Variantly (Devarim 6:4) "the L-rd is our G-d": in this world; "the L-rd is One": in the world to come. And thus is it written (Zechariah 14:9) "And the L-rd will be the King over all the land. On that day the L-rd will be One and His name will be One."
(Devarim 6:5) "And you shall love the L-rd your G-d": Act (i.e., serve) out of love. There is a difference between acting out of love and acting out of fear. If one acts out of love, his reward is doubled. It is written (Ibid. 6:13) "The L-rd your G-d shall you fear, and Him shall you serve." One may fear his friend, but if he belabors him, he may leave him. But you, act out of (absolute) love. And there is no (absolute) love in the place of (i.e., co-existing with [absolute]) fear, and no (absolute) fear in the place of (absolute) love except vis-à-vis the Holy One Blessed be He. (So that if one loves Him absolutely, it follows that he fears him absolutely, and his reward is doubled.)