Our dear brother,
1. The essence of this definition is not the denial of reason. However, if a person takes reason as a basis in the things that need to be believed and accepts what agrees with reason and denies what does not, this is not called faith . However, there is no harm in proving things of faith with reason.
This statement is not to deny the importance of reason, but to show the mistake made by those who deny that they do not see it as compatible with reason and experience.
2. For example, the existence of the afterlife and the non-existence of the dead are among the principles of faith. It’s like someone denying it by saying, “I can’t see this with my eyes.”
3. Yes, the door of repentance is open until death. Everyone can repent at any time, unless they die denying one of the principles of faith.
Man was created suitable to do both good and evil. That’s why he may commit sins, willingly or unintentionally, from time to time. On this subject, in the Holy Quran,
“Allah forgives all the sins of those He wishes, except death due to shirking Him.” (An-Nisa, 48/116)
By saying this, he states that he can forgive no matter what sin it is.
As a matter of fact, whenever a person who has spent his life in disbelief repents and comes to faith, his repentance is accepted. Islamic history is full of examples of these