His saying {then He will bring you back to life} is the third life and death. Finally, His saying {then to Him you will be returned} refers to the fluctuations of your "garments" (bodies) according to the merit of your deeds across many lives. This proves reincarnation.
I offer the following as another explanation of this verse, in a different manner: since death was mentioned before life in the verse
{How can you disbelieve in Allah when you were lifeless and He brought you to life...} 1 , and since it appeared in the past tense ({you were lifeless}) Since it was a predestined measure that ended a preexisting life—meaning there was a prior life implied by "you were lifeless"—this signifies the existence of life before that death. The establishment of life before death is called the state of creation by the word "Be" (Kun). This view is supported by the explicit statement: {And He is the one who gave you life; then He causes you to die} 2 , meaning life began and then death followed it, with a delay in steps. The coordinating conjunction "then" (thumma), which is repeated as a separator between "causes you to die" and "gives you life," indicates order, succession, and a temporal lapse between the act of causing death and the second bringing to life. Subsequently, the return to the Creator occurs: {then to Him you will be returned}.