Kriya

A kriya is a set of yoga exercises that form a coherent finished sequence. It has been designed and refined during ages by wise yogi until it produced the desired impact on body and mind for every practicioner. So you follow it literally.

Compare it with the recipe of your grandmother's delicious cake. If she bakes the cake without eggs and then pours the raw eggs over it at the end, you would get an unappetizing result.