How does Allah punish us for a sin that is limited in time?

Peace be upon you, Why does the Companion of the Time not appear in a video tape so that his lovers’ hearts may become assured and that the proof be put upon the deniers and his location would not be disclosed? What is the sin of the ones whom the Qur’an did not reach? How does Allah punish us and He is the Most Benevolent, the Most Merciful, for a sin that is limited in time with a punishment that is unlimited forever (The Fire, dwelling in it forever)?