Does the inability to imagine the torment of Hell or the bliss of Paradise, or to see the Prophet, may Allah bless him and grant him peace, therein, indicate a weakness of faith?

The inability to imagine torment or bliss in the afterlife does not diminish faith, because it is of the unseen. Allah has informed us of the categories of bliss and torment and has given us examples in this world to understand the discourse and to strive for Paradise and flee from punishment. We understand what Allah has told us of the unseen through what is commonly shared between it and what is in this world, even if the realities of the afterlife differ from this world except in names. What is important is to be affected and to fear punishment and to hope for otherworldly bliss.