What is the meaning of the Almighty's saying: "And this secure city" (wa hādhā al-baladi al-amīn)? And why was it described as "al-amīn" (secure/trustworthy) and not "al-āmin" (safe)? Is there a linguistic benefit in that?

The "Secure City" (Al-Balad Al-Amin) in the Qur’an is the honorable Mecca, and exegetes have concurred on this. The meaning of "Al-Amin" is "secure" or "safe," either as an active participle (fa'il) meaning "safe" (amin), or as a passive participle (maf'ul) meaning "secured" (ma'mun), used for hyperbole to emphasize its indication of security.