I do not agree with the view that the world is an illusion, mithya. The Brahman is here as well as in the supracosmic Absolute. The thing to be overcome is the Ignorance which makes us blind and prevents us from realising Brahman in the world as well as beyond it and the true nature of existence.
The Shankara knowledge is, as your Guru pointed out, only one side of the Truth; it is the knowledge of the Supreme as realised by the spiritual Mind through the static silence of the pure Existence. It was because he went by this side only that Shankara was unable to accept or explain the origin of the universe except as illusion, a creation of Maya. Unless one realises the Supreme on the dynamic as well as the static side, one cannot experience the true origin of things and the equal reality of the active Brahman.
The Shakti or Power of the Eternal becomes then a power of illusion only and the world becomes incomprehensible, a mystery of cosmic madness, an eternal delirium of the Eternal. Whatever verbal or ideative logic one may bring to support it, this way of seeing the universe explains nothing; it only erects a mental formula of the inexplicable. It is only if you approach the Supreme through his double aspect of Sat and Chit-Shakti, double but inseparable, that the total truth of things can become manifest to the inner experience. This other side was developed by the Shakta Tantriks. The two together, the Vedantic and the Tantric truth unified, can arrive at the integral knowledge.
But philosophically this is what your Guru’s teaching comes to and it is obviously a completer truth and a wider knowledge than that given by the Shankara formula. It is already indicated in the Gita’s teaching of the Purushottama and the Parashakti (Adya Shakti) who become the Jiva and uphold the universe. It is evident that Purushottama and Parashakti are both eternal and are inseparable and one in being; the Parashakti manifests the universe, manifests too the Divine in the universe as the Ishwara and Herself appears at His side as the Ishwari Shakti. Or, we may say, it is the Supreme Conscious Power of the Supreme that manifests or puts forth itself as Ishwara Ishwari, Atma Atma-shakti, Purusha Prakriti, Jiva Jagat. That is the truth in its completeness as far as the mind can formulate it. In the supermind these questions do not even arise: for it is the mind that creates the problem by creating oppositions between aspects of the Divine which are not really opposed to each other but are one and inseparable.
This supramental knowledge has not yet been attained, because the supermind itself has not been attained, but the reflection of it in intuitive spiritual consciousness is there and that was what was evidently realised in experience by your Guru and what he was expressing in mental terms in the quoted passage. It is possible to go towards the knowledge by beginning with the experience of dissolution in the One, but on condition that you do not stop there, taking it as the highest Truth, but proceed to realise the same One as the supreme Mother, the Consciousness-Force of the Eternal. If, on the other hand, you approach through the Supreme Mother, she will give you the liberation in the silent One also as well as the realisation of the dynamic One, and from that it is easier to arrive at the Truth in which both are one and inseparable. At the same time, the gulf created by mind between the Supreme and His manifestation is bridged, and there is no longer a fissure in the truth which makes all incomprehensible. If in the light of this you examine what your Guru taught, you will see that it is the same thing in less metaphysical language.
As for Adesh, people speak of Adesh without making the necessary distinctions, but these distinctions have to be made. The Divine speaks to us in many ways and it is not always the imperative Adesh that comes. When it does, it is clear and irresistible, the mind has to obey and there is no question possible, even if what comes is contrary to the preconceived ideas of the mental intelligence. It was such an Adesh that I had when I came away to Pondicherry. But more often what is said is an intimation or even less, a mere indication, which the mind may not follow because it is not impressed with its imperative necessity. It is something offered but not imposed, perhaps something not even offered but only suggested from the Truth above.