p. 278
शिष्यवृत्तिक्रमेणैव ‘आचार्ययोनिमिह’ इत्यादिनोक्तक्रमेण शुचिः विद्यामाप्नोति यत्, तत् ब्रह्मचर्यं तस्यास्य प्रथमः
In plain words
By keeping to the student's way of living, step after step, in the order set out in the passage that begins "the teacher's womb, here" — a person made pure comes into knowledge. That is brahmacarya. And this is the first part of it.
Close to the Sanskrit
By the very sequence of the disciple's conduct, by the order stated in the passage beginning 'the teacher's womb here', the pure one obtains knowledge — that is brahmacarya; of that, of this, the first [part].