Reb Shmuel Gronem Esterman, renowned Mashpia in the times of the Rebbe Maharash and the Rebbe Rashab, taught:
Chassidus explains that Leah and Rochel correspond to thought and speech, respectively. It is written, “G–d saw that Leah was hated” (Bereishis 29:31). This means that people are willing to learn Chassidus verbally, but are lazy when it comes to thinking Chassidus. The verse continues, “and He opened her womb [whereas Rachel was barren].” This means that the birth and revelation of the divine light comes specifically through thought. This will suffice for an understanding person.
Shemu’os V’Sipurim, Vol. 1, p. 180.
Summary: If we want G–dliness to shine in our souls, it is not enough to learn Chassidus; we must engage in Hisbonenus—meditation on concepts in Chassidus.
Comment: The reason that Hisbonenus is typically more neglected that study is apparently that it is much more difficult, as discussed here.