In The Name of Allaah, The Most Merciful, The Besstower of Mercy.
Imaam As-Sadi [may Allaah have mercy upon him] said:
It (i.e. Islam) is the religion that whoever embodies it, Allaah gathers for him (or her) outward and inner beauty, perfect morals and deeds. Allaah said: [ومن أحسن دينا ممن أسلم وجهه لله وهو محسن – And who can be better in religion than one who submits himself to Allah (i.e. follows Allah’s Religion of Islamic Monotheism); and he is a Muhsin (a good-doer)]. [Surah An-Nisaa. Aayah 125]
There is none better than one who is sincere to Allaah, benevolent to Allaah’s servants, and sincere in his (or her) adherence to Allaah’s laws, which is the best of laws and the most upright methodology, so his (or her) heart becomes imbued with sincerity and sound Islamic monotheism, and his morals and actions are based on upright guidance and sound rectification. Allaah said:
[صبغة الله ومن أحسن من الله صبغة ونحن له عابدون – The Religion (ordained and chosen by) Allah (for humankind and jinn (i.e. Islam) and which religion can be better than the One (ordained and chosen) by Allah? And we are His worshippers].
Commentary: This religion is (an upright) adornment for a person- inwardly and outwardly. In a supplication of the Prophet [peace and blessings of Allaah be upon him], he said: [اللَّهُمَّ زَيِّنَّا بِزِينَةِ الْإِيمَانِ – O Allah! Adorn us with the adornment of Eemaan (i.e. sound faith)]. (see footnote a). And in Surah Al-Hujuraat, Allaah said: [ وَزَيَّنَهُ فِي قُلُوبِكُمْ – And has beautified it (i.e. sound faith) in your hearts]. [Surah Al-Hujuraat. Aayah 7] (see footnote b)
So, it (i.e. Islam) is an (upright) adornment for the person. Allah said: [وَلِبَاسُ ٱلتَّقۡوَىٰ ذَٲلِكَ خَيۡرٌ۬ۚ – And the raiment of piety (i.e. the piety in the hearts that stops a person from evil), that is what is better]. [Surah Al-A’raaf. Verse 26]
It (i.e. Islam) is the most perfect adornment, the greatest beauty and the best adornment. The outward deeds of a believer are the righteous deeds, and what is concealed in the heart are the correct beliefs, such as (praiseworthy) shyness, hope in Allaah, love of Allaah, being merciful to the people and other deeds of this great religion. It is a religion that rectifies the inner self and the apparent deeds – a means to upright rectification of the hearts and deeds. (see footnote c) (1)
Footnote a: Adornment with sound faith includes beautification of the heart with sound creed and noble deeds of the heart; beautification of the tongue with remembrance of Allaah and recitation of the Qur’aan, enjoining good and forbidding evil and so forth; beautification of the limbs with righteous deeds and deeds that draws a person close to Allaah. [Fiqhul Adiyah Wal Adkaar. Vol 3. Pages 165-169]
Footnote b: Imaam Ibnul Qayyim[may Allaah have mercy upon him] said: Your love for sound faith, desire for it and its beautification in your hearts is not from yourselves; rather it is Allaah who placed it in your hearts. He is the one who made it preferable and pleasing to you; therefore do not put yourself before My Messenger-neither speak until he speaks nor act until he commands you. The one (i.e. Allaah) who made you love Imaan is the most knowledgeable concerning what is of benefit for His slaves than yourselves. And had it not been for the blessings of Allaah, your souls would not have yielded to sound faith. Neither would have sound faith been (attained) through your consultation and bestowed by yourselves, nor would you have given it precedence because your souls are unable and weak to (do so), and cannot reach it. [Madaarij As-Saalikeen 1/414-415]
Footnote c: Allaah said:
يَـٰبَنِىٓ ءَادَمَ قَدۡ أَنزَلۡنَا عَلَيۡكُمۡ لِبَاسً۬ا يُوَٲرِى سَوۡءَٲتِكُمۡ وَرِيشً۬اۖ وَلِبَاسُ ٱلتَّقۡوَىٰ ذَٲلِكَ خَيۡرٌ۬ۚ ذَٲلِكَ مِنۡ ءَايَـٰتِ ٱللَّهِ لَعَلَّهُمۡ يَذَّكَّرُونَ
O Children of Adam! We have bestowed raiment upon you to cover yourselves (screen your private parts, etc.) and as an adornment, and the raiment of righteousness, that is better. Such are among the Ayat (proofs, evidences, verses, lessons, signs, revelations, etc.) of Allah, that they may remember (i.e. leave falsehood and follow truth ). [Surah Al-A’raaf. Verse 26]. Read more here regarding inner and outer adornment: https://salaficentre.com/wp-content/uploads/2021/07/Admonitions-of-The-Scholars-Regarding-Good-Manners.pdf
[Ref 1: From 27mins 16secs to 31mins 03secs https://www.al-badr.net/detail/8LD6UgwQrZ . paraphrased]