In their original form rituals are what we need to do because they are divine requirements. In a traditional religious community, dedicated to fulfilling the word of God as group members understand it, the rituals are a vital part of the whole corpus of behavioral rules. From a sociological-anthropological perspective they serve to bind and coordinate the actions of the individuals in the community.
If individuals evolve away from the fundamental belief in literal divine revelation, the rituals are not necessarily discarded, but the understanding of them changes. They come to be seen as a kind of aesthetic, serving to bolster the community’s strength – like beautiful poems recited and songs sung together in harmony (literal and figurative).
But, over time, though some rituals may be retained longer than others, it is likely that many will be abandoned and others “diluted” to suit their more secular human purpose.