question #1 Sahih al-Bukhari 781, Book 10, Hadith 176 : What is the significance of saying ‘Amin’ during prayer in Islam?

Allah’s Messenger (ﷺ) said, “If any one of you says, “Amin” and the angels in the heavens say “Amin” and
the former coincides with the latter, all his past sins will be forgiven.”