I had an opportunity to teach a group of boys a number of years ago who attended Sydney Grammar School. The boys’ music department teacher was a student of mine, and he felt that these boys who were music students would benefit from some sessions.
I prepared my lessons for a group of 14 boys, but only 11 of them came along for yoga. Apparently some of the parents thought of yoga as a religion and they didn’t want their sons to be exposed to some Indian transcendental cult.
It would have been interesting to talk to these parents about what they did think yoga was because, to my mind, yoga is non-denominational and non-religious.
If you’ve studied yoga a little, you might have heard that the word yoga = union, derived from ‘yug’ meaning ‘to join’ in Sanskrit. Join what? The various aspects of ourselves that were never really divided in the first place.
As for the notion of religion in the Sutra, when Patanjali speaks of Ishvara, he doesn’t necessarily mean God, although this is often a way that word is translated.
Chip Hartranft’s explanation is the one that resonates best with me. He says:

Isvara…is neither god nor purusa in the usual sense but rather a divine mirror toward which people throughout the ages might turn to catch a glimpse of their own true nature and its possibility of complete freedom from prakritic entrapment.*

In other words, through yoga practice, we can have the direct experience of ourselves beyond the false identities that come from our conditioning – identities that arise from the way we are buffeted about between aversion and attraction.  The opportunity is that we become whole or more accurately realise our underlying wholeness.
Those school boys had a little taste of yoga and I would have hoped that it gave them an appetite for more. As a yoga teacher, I don’t always know the results of my planting seeds, but I that trust in fertile ground they will grow.

Tapah svadhyaya Isvarapranidhanani kriyayogah

Burning zeal in practice, self-study and study of scriptures, and surrender to God are the acts of yoga.**
*The Yoga Sutra of Patanjali, Chip Hartranft.
**Light on the Yoga Sutras of Patanjali, B.K.S. Iyengar.