I.1- atha yogānuśāsanam

The first Sūtra introduces the subject matter, as the oral requires. In the convention if ancient Sanskrit literature, the first word atha, carries the connotation of a prayer, both for an auspicious beginning and a successful conclusion to the study which follows. 

Here begins the authoritative instruction on Yoga.

Through the term anuśāsanam, Pataïjali indicates that, while the subject matter is of ancient origin and he is not the source. Rather, he has studied and practiced it to an appropriate depth under his own teacher and is now competent to share his understanding with his disciples. His style will be in a manner suitable for them to transmit this knowledge in turn to their own disciples through the traditional oral method of teaching transmission.