Names and Attributes of Allaah,- What is the meaning of Allaah’s name al-Mu’min (the Giver of Security)? Praise be to Allaah. Allaah is al-Mu’min, the One Who will fulfil the promise to the sincere. He calls His slaves to believe in Him and He has control over the security of His creation in this world and in the Hereafter. And He declares Himself to be One, as He says (interpretation of the meaning): “Allaah bears witness that Laa ilaaha illa Huwa (none has the right to beworshipped but He)” [Aal ‘Imraan 3:18] Al-Mu’min is the one Who accepts His believing slaves, i.e., He accepts their faith and sincerity and makes them steadfast. And He fulfils His promise to His slave of reward. He gives security to His close friends (awliya’) bykeeping them safe from His punishment and torment. So they are safe, and no one is safe except those to whom He grants safety. He fulfils what His slaves think of Him and never allows their hopes to be dashed. He is the one Who declared Himself to be One,

What is the meaning of Allaah's name al-Mu'min (the Giver of Security)?
Praise be to Allaah.
Allaah is al-Mu'min, the One Who will fulfil the promise to the
sincere. He calls His slaves to believe in Him and He has control over
the security of His creation in this world and in the Hereafter. And
He declares Himself to be One, as He says (interpretation of the
meaning):
"Allaah bears witness that Laa ilaaha illa Huwa (none has the right to
beworshipped but He)" [Aal 'Imraan 3:18]
Al-Mu'min is the one Who accepts His believing slaves, i.e., He
accepts their faith and sincerity and makes them steadfast. And He
fulfils His promise to His slave of reward.
He gives security to His close friends (awliya') bykeeping them safe
from His punishment and torment. So they are safe, and no one is safe
except those to whom He grants safety. He fulfils what His slaves
think of Him and never allows their hopes to be dashed.
He is the one Who declared Himself to be One, as He says
(interpretation of the meaning):
"And your Ilaah (God) is One Ilaah (God — Allaah)" [al-Baqarah 2:163]
He is the One Who guarantees not to treat His creation unjustly, and
the one who does not deserve His punishment is safe from it.
He is the One Who will accept the testimony of His Muslim slaves on
the Day of Resurrection, when the nations will beasked whether the
Messengers conveyed the Message. Allaah says (interpretation of the
meaning):
" [the Prophet (peace and blessings of Allaah be upon him)] has faith
in the believers" [al-Tawbah 9:61]
All of these attributes belong to Allaah becauseHe spoke the truth of
Tawheed to which He calls His slaves. He guarantees that His slaves
will not be treatedunjustly [in the Hereafter] and promises Paradise
to those who believe in Him and Hell to those who disbelieve in Him.
And He is the OneWho keeps His promise.
Sharh Asmaa' Allaah ta'aala al-Husna by Dr. Hissah al-Sagheer, p. 220