What is need of transmission modes in Serial Peripheral Interface
SPI module on a microcontroller can be used to talk to several slave chips that might use different modes. For instance one chip might require rising clock edges to load data, and another chip might require falling clock edges to load data. The communication has to use the right settings for each chip or it fails to transfer data reliably, so there is a need to select which settings to use. So the last line you are confused about just means that one settings are used with one chip and between transmissions settings can be changed so another settings can be used with another chip.