The device reads and writes data in edges of the clock, unless there is a clock there can be no data transfer in the SPI lines and the clock can only be provided by the master so what you do is send a dummy byte to provide the necessary clock and the data are transferred from the eeprom to the mcu during that clock edges, the data that you send to the slave during that dummy write are ignored, only the data send from the slave to the master are important in this phase.
Alex