Not only the faith in Ishwara but also an attitude of surrendering the self to the Ishwara (or devotion to Ishwara) is very important to succeed in the path of Yoga because there are several obstacles in this path which will vanish by meditation on Om.
Following are some qualities required to march in this path: (Refer the first chapter of Yoga sutras)
श्रद्धा-वीर्य-स्मृति-समाधि-प्रज्ञा-पूर्वक इतरेषाम् ॥२०॥
- To others (this Samadhi) comes through faith, energy, memory, concentration, and discrimination of the real.
As said in next Sutras:
- Success is speedy for the extremely energetic.
- The success of Yogis differs according as the means they adopt are mild, medium, or intense.
- Or by devotion to Ishvara.
Following sutra states the obstacles in the path:
- Disease, mental laziness, doubt, lack of enthusiasm, lethargy, clinging to sense-enjoyments, false perception, non-attaining concentration, and falling away from the state when obtained, are the obstructing distractions.
And by meditating on Om, one attains the ability to overcome these obstacles:
- From that is gained (the knowledge of) introspection, and the destruction of obstacles.
Now talking about having doubt on what has been said in Yoga sutras, When the practitioner focuses his/her mind on the objects suggested in sutras, s/he starts getting extraordinary experience which clears the doubts and establishes the faith according to Swami Vivekananda:
विषयवती वा प्रवृत्तिरुत्पन्ना मनसः स्थितिनिबन्धिनी ॥३५॥
35. Those forms of concentration that bring extraordinary sense-perceptions cause perseverance of the mind.
This naturally comes with Dhâranâ, concentration; the Yogis say, if the mind becomes concentrated on the tip of the nose, one begins to smell, after a few days, wonderful perfumes. If it becomes concentrated at the root of the tongue, one begins to hear sounds; if on the tip of the tongue, one begins to taste wonderful flavours; if on the middle of the tongue, one feels as if one were coming in contact with something. If one concentrates one's mind on the palate, one begins to see peculiar things. If a man whose mind is disturbed wants to take up some of these practices of Yoga, yet doubts the truth of them, he will have his doubts set at rest when, after a little practice, these things come to him, and he will persevere.
So, when one starts believing in Yoga Sutras, s/he will also establish a faith on Ishwara that eventually can lead to realization of the Ishwara.
After all this path of Yoga has the feature of validating all the things by realizing them, Ishwara can also be realized and attained but one need to have a stable mind to success and without keeping faith on Ishwara (or having doubts) one will face the issue of having a disturbed mind which is not eligible to march further in the right direction.