Resting phase is the most active phase in cell division. This phase is is also known as interphase. It does not show the charcateristic changes of a deviding cell, it carry on the vital activities of the other phases. read more
Because in Interphase all types of proteins are formed which are required for division of cell,all organelles duplicate,DNA replicate,ATP is formed etc etc. In short preparation for division of cell is done in Interphase. Hence it is the most active phase of cell cycle. Hope it helps. read more