What is the difference between one who falls into disbelief while ignorant and one who does so while knowledgeable?

The Shaykh : And for that reason, I feared that you would declare him a disbeliever, even though he is ignorant, although he intended this disbelief.

The questioner : Yes.

The Shaykh : But he is ignorant that it is disbelief according to the Shari'ah. In that case, we say that he does not become a disbeliever. However, if he is knowledgeable, then there is no difference between him, whom I described as ignorant, and the other, whom I described as knowledgeable, because both share the knowledge that this disbelief is disbelief according to the Shari'ah. Therefore, this person has no excuse.