Atmega16 SPI Questions
From the datasheet:


  ... writing a byte to the SPI Data Register starts the SPI clock generator, and the hardware shifts the eight bits into the Slave. After shifting one byte, the SPI clock generator stops, setting the end of Transmission Flag (SPIF).


Writing the byte is what initiates the SPI transfer. If you don't write the byte then the transfer won't start and hence can never finish.