When a person learns Torah, just as the physical energy of uttering the words does not vanish, the spiritual content of those words also does not vanish.
When a person reads a verse or studies a page of Talmud, it becomes a form of spiritual reality.
This spiritual reality is linked to the person, to what and how he studied, in a relationship of cause and effect.
It now remains, and it operates according to its place and magnitude.
If the person studied Torah without intention for the sake of Heaven, it belongs to the externality of the worlds.
This generates angels of a lower level, roughly formed angels that are only undirected, blind forces.
This is a spiritual reality of holiness that has no essential inner spirit within it, and all it contains is the intellect that was invested into the study, the natural heat of committing the action, and nothing more.
Rabbi Adin Steinsaltz