Ishwara has a specialized meaning in the Yoga Darsana.
24. Ishvara (the Supreme Ruler) is a special Purusha, untouched by misery, actions, their results, and desires.
We must again remember that the Pâtanjala Yoga philosophy is based upon the Sankhya philosophy; only in the latter there is no place for God, while with the Yogis God has a place. The Yogis, however, do not mention many ideas about God, such as creating. God as the Creator of the universe is not meant by the Ishvara of the Yogis. According to the Vedas, Ishvara is the Creator of the universe; because it is harmonious, it must be the manifestation of one will. The Yogis want to establish a God, but they arrive at Him in a peculiar fashion of their own. They say:
तत्र निरतिशयं सर्वज्ञत्वबीजम् ॥२५॥
25. In Him becomes infinite that all-knowingness which in others is (only) a germ.
The mind must always travel between two extremes. You can think of limited space, but that very idea gives you also unlimited space. Close your eyes and think of a little space; at the same time that you perceive the little circle, you have a circle round it of unlimited dimensions. It is the same with time. Try to think of a second; you will have, with the same act of perception, to think of time which is unlimited. So with knowledge. Knowledge is only a germ in man, but you will have to think of infinite knowledge around it, so that the very constitution of our mind shows us that there is unlimited knowledge, and the Yogis call that unlimited knowledge God.
स पूर्वेषामपि गुरुः कालेनानवच्छेदात् ॥२६॥
26. He is the Teacher of even the ancient teachers, being not limited by time.
It is true that all knowledge is within ourselves, but this has to be called forth by another knowledge. Although the capacity to know is inside us, it must be called out, and that calling out of knowledge can only be done, a Yogi maintains, through another knowledge. Dead, insentient matter never calls out knowledge, it is the action of knowledge that brings out knowledge. Knowing beings must be with us to call forth what is in us, so these teachers were always necessary. The world was never without them, and no knowledge can come without them. God is the Teacher of all teachers, because these teachers, however great they may have been — gods or angels — were all bound and limited by time, while God is not. There are two peculiar deductions of the Yogis. The first is that in thinking of the limited, the mind must think of the unlimited; and that if one part of that perception is true, so also must the other be, for the reason that their value as perceptions of the mind is equal. The very fact that man has a little knowledge shows that God has unlimited knowledge. If I am to take one, why not the other? Reason forces me to take both or reject both. If I believe that there is a man with a little knowledge, I must also admit that there is someone behind him with unlimited knowledge. The second deduction is that no knowledge can come without a teacher. It is true, as the modern philosophers say, that there is something in man which evolves out of him; all knowledge is in man, but certain environments are necessary to call it out. We cannot find any knowledge without teachers. If there are men teachers, god teachers, or angel teachers, they are all limited; who was the teacher before them? We are forced to admit, as a last conclusion, one teacher who is not limited by time; and that One Teacher of infinite knowledge, without beginning or end, is called God.
तस्य वाचकः प्रणवः ॥२७॥
27. His manifesting word is Om.
Every idea that you have in the mind has a counterpart in a word; the word and the thought are inseparable. The external part of one and the same thing is what we call word, and the internal part is what we call thought. No man can, by analysis, separate thought from word. The idea that language was created by men — certain men sitting together and deciding upon words, has been proved to be wrong. So long as man has existed there have been words and language. What is the connection between an idea and a word? Although we see that there must always be a word with a thought, it is not necessary that the same thought requires the same word. The thought may be the same in twenty different countries, yet the language is different. We must have a word to express each thought, but these words need not necessarily have the same sound. Sounds will vary in different nations. Our commentator says, "Although the relation between thought and word is perfectly natural, yet it does not mean a rigid connection between one sound and one idea." These sounds vary, yet the relation between the sounds and the thoughts is a natural one. The connection between thoughts and sounds is good only if there be a real connection between the thing signified and the symbol; until then that symbol will never come into general use. A symbol is the manifester of the thing signified, and if the thing signified has already an existence, and if, by experience, we know that the symbol has expressed that thing many times, then we are sure that there is a real relation between them. Even if the things are not present, there will be thousands who will know them by their symbols. There must be a natural connection between the symbol and the thing signified; then, when that symbol is pronounced, it recalls the thing signified. The commentator says the manifesting word of God is Om. Why does he emphasise this word? There are hundreds of words for God. One thought is connected with a thousand words; the idea "God" is connected with hundreds of words, and each one stands as a symbol for God. Very good. But there must be a generalization among all time words, some substratum, some common ground of all these symbols, and that which is the common symbol will be the best, and will really represent them all. In making a sound we use the larynx and the palate as a sounding board. Is there any material sound of which all other sounds must be manifestations, one which is the most natural sound? Om (Aum) is such a sound, the basis of all sounds. The first letter, A, is the root sound, the key, pronounced without touching any part of the tongue or palate; M represents the last sound in the series, being produced by the closed lips, and the U rolls from the very root to the end of the sounding board of the mouth. Thus, Om represents the whole phenomena of sound-producing. As such, it must be the natural symbol, the matrix of all the various sounds. It denotes the whole range and possibility of all the words that can be made. Apart from these speculations, we see that around this word Om are centred all the different religious ideas in India; all the various religious ideas of the Vedas have gathered themselves round this word Om. What has that to do with America and England, or any other country? Simply this, that the word has been retained at every stage of religious growth in India, and it has been manipulated to mean all the various ideas about God. Monists, dualists, mono-dualists, separatists, and even atheists took up this Om. Om has become the one symbol for the religious aspiration of the vast majority of human beings. Take, for instance, the English word God. It covers only a limited function, and if you go beyond it, you have to add adjectives, to make it Personal, or Impersonal, or Absolute God. So with the words for God in every other language; their signification is very small. This word Om, however, has around it all the various significances. As such it should be accepted by everyone.
The Complete Works of Swami Vivekananda, Volume 1, Patanjali Yoga Sutra I.24-27