Al-Mu’min ( The Testifier, The Giver of security):

This great name of Allah has come in the Holy Quran only once and that is in the verse 23 of surah Al-Hashar. The translation of the verse is:

(59:23) He is Allah: there is no god but He: the King,³⁶ the Holy,³⁷ the All-Peace,³⁸ the Giver of security,³⁹ the Overseer,⁴⁰ the Most Mighty,⁴¹ the Overpowering,⁴² the All-Great.⁴³ Exalted is He from whatever they associate with Him.

Exp-note 39:

39. The word Al-Mu’min is derived from amn, which means to secure from fear, and Mu’min is the one who provides security to others. Allah has been called Al-Mumin in the sense that He provides security to His creatures. His creatures are secure from the fear that He would ever wrong them, or deprive them of their rights, or allow their rewards to go to waste, or would violate the promises He has made with them. Then, since no object has been mentioned with this subject, but the epithet of Al-Mumin has been used absolutely, it automatically gives the meaning that His security comprehends the entire universe and all that it contains. 

The other meanings of this name are:

The name is also related with the word “al-eemaan” which means to believe and testify, also the one who confirms (authorizes true) the eemaan of Muslims.

So Allah is Al-Mu’min in the sense that Allah admires Himself as One Single and Unique God. Mujaahid rahmatullahi alaihi said:  Al-Mu’min is the One Who testified Himself to be One by saying; “Shahida-Allaho annahu laa ilaha illa huwa” (Allah witnessed /testified that there is no God except Him). This is a part of the verse 18 of the surah Aali-Imraan. This is the greatest testimony from the Greatest Witness (Allah) on the most important of the object which is Tawheed of Allah and the purifying of the Deen (religion) for Him. Tawheed means to believe in the absolute Oneness of God.      

It comes in the Al-Tirmidhi, Ibn. Maajah and others that Abu Hurairah and abu Sa-eed testified that Allah’s Messenger salla Allaho alaihi wa sallam said, “ when a servent says ‘laa ilaha ill Allaho, wa-Allaho akbar’ Allah Tabaarak wa Ta’ala says ‘ My servant said the truth, there is no God except Me and I am the Greatest’. And when (the servant) says, ‘laa ilaha illa Allaho wahdahu’ (Allah) says, ‘My servant said the truth, there is no God but I, the One’. And when he ( the servant) says, ‘laa ilaha illa Allaho wahdahu laa shareeka lahu’ (Allah) says, ‘My servant said the truth, there is no God but I, there is no partner with Me’. And when (the servant ) said, ‘laa ilaha illa Allaho lahul mulku wa lahul hamd’ (Allah )says, My servant said the truth, there is no God but I, Mine is the Kingdom and for Me are the Praises. And when (the servant) said, ‘‘laa ilaha illa Allaho   
wa laa hawla wa laa quwwata illa billah (bi-Allah)’ (Allah) says, ‘My servant said the truth, there is no God but I and there is no power and no strength but with Me’.

Thus it is the great testimony from Allah for the absolute Oneness of Himself and also the confirmation of the testifying of the servants. This confirmation by Allah of their testimonies about tawheed and other articles of faith becomes a proof and evidence to help them on the Day of Judgement. Ibn Al-Qayyim rahmatullahi alaihi said that from His Names one is Al-Mu’min which in one of the commentaries, is considered to be Al-Musaddiq. Al-Musaddiq means the One Who confirms the truth of the truthful and provides evidence of their truthfulness. So Allah, the Al-Mu’min Al-Musaddiq confirmed the truthfulness of His Prophets and Messengers alayhim salaam. Allah, due to His Attribute Al-Mu’min, revealed evidences to prove the truth of His messengers, that whatever they said regarding the religion, is true and is from Allah. That the Divine Books (e.g. the Holy Quraan) is truly the Revelation of Allah. To understand this point see the translation of the following Verses of the Holy Quraan:

Surah Fusilat verses 52 and 53 (translation only):

(41:52) Say, “Have you considered: if the Qur’an is from Allah and you disbelieved in it, who would be more astray than one who is in extreme dissension?”

(41:53) We will show them Our signs in the horizons and within themselves until it becomes clear to them that it is the truth. But is it not sufficient concerning your Lord that He is, over all things, a Witness?