Here is the full passage from Sri Aurobindo’s letter to Barin in April 1920.
‘If the spiritual force is poured into these impure forms—the wine of the spirit into these unbaked vessels—the imperfect things will break apart and spill and waste the wine. Or else the spiritual force will evaporate and only the impure form remain. It is the same in every field of activity. I could use my spiritual influence; it would give strength to those who received it and they would work with great energy. But the force would be expended in shaping the image of a monkey and setting it up in the temple of Shiva. If the monkey is brought to life it may grow powerful, and in the guise of the devotee Hanuman do much work for Rama—so long as the life and strength remain. But in the temple of India we want not Hanuman but the Godhead, the Avatar, Rama himself.’
(Ref. https://incarnateword.in/cwsa/09/letters-to-barin#p11)
What Sri Aurobindo is referring to is the application of the tremendous spiritual force he had gathered by his tapasya. He is not keen to pour it in vessels that are not ready. Doing so might either break them or else, at best, prepare powerful instruments like Hanuman. But he is not satisfied with that. He wants human beings to grow into the image of God Himself, to become Divine and manifest the perfect Divine Nature, rather than be only the instrument.
Affectionately,
Alok Da
