In The Name of Allaah, The Most Merciful, The Bestower of Mercy
Allaah [The Most High] said:
وَمَن يُسۡلِمۡ وَجۡهَهُ ۥۤ إِلَى ٱللَّهِ وَهُوَ مُحۡسِنٌ۬ فَقَدِ ٱسۡتَمۡسَكَ بِٱلۡعُرۡوَةِ ٱلۡوُثۡقَىٰۗ وَإِلَى ٱللَّهِ عَـٰقِبَةُ ٱلۡأُمُورِ
And whosoever submits his face [himself] to Allaah while he is a Muhsin [good doer], then he has grasped the most trustworthy handhold [Laa ilaaha ill-Allah (none has the right to be worshipped except Allaah)]. And to Allaah return all matters for decision. [Surah Luqmaan. Aayah 22]
[وَمَن يُسۡلِمۡ وَجۡهَهُ ۥۤ إِلَى ٱللَّهِ – And whosoever submits his face (himself) to Allah]- Meaning: This is the one who [willingly and sincerely] humbles and submits himself to Allaah [The Most High], sincerely carries out acts of worship and keeps away from what Allaah has forbidden; [وَهُوَ مُحۡسِنٌ۬ – while he is a good-doer]-Meaning: A good doer in the religion of Islaam, who [sincerely] carries out acts of worship that have been legislated by Allaah [The Most High] and in accordance with the authentic Sunnah of the Messenger [sallal-laahu-alayhi-wasallam]; or that person who [willingly and sincerely] submits to Allaah by carrying out legislated acts of worship in a manner as if he or she is seeing Allaah, even though [that is not possible in this worldly life], but knows that Allaah sees him or her; or that one who [willingly and sincerely] submits to Allaah by fulfilling the rights of Allaah [i.e. worships Allaah alone, fulfil Allaah’s commands and keeps away from what Allaah has forbidden] and fulfils the rights of the people. All the above explanations mean the same thing, because the performers of these [righteous deeds] accept such deeds and perform them perfectly. However, the only difference between them is the [level of striving and sincerity of each person].
Therefore, whoever does this, [i.e. willingly submits] to Allaah, whilst being a good doer in Islam], then such a person has truly submitted to Allaah [The Most High] and is one who has ‘Grasped the most trustworthy hand-hold [i.e. that none has the right to be worshipped except Allaah]’, which will make a person steadfast and lead to safety – safeguards a person from destruction and lead to success through every path of good.
On the other hand, whoever does not submit to Allaah willingly and is not a good doer based on the acts of worship legislated by Allaah and are to be performed in accordance with the authentic Sunnah of the Messenger [sallal-laahu-alayhi-wasallam], then indeed such a person has not grasped the most trustworthy handhold.
And when it is case that such a person is not among those holding to this most trustworthy handhold, then indeed his or her end cannot be anything else but destruction. [وَإِلَى ٱللَّهِ عَـٰقِبَةُ ٱلۡأُمُورِ – And to Allah return all matters for decision]- Meaning: All matters will return to Allaah, so that He will judge between mankind and jinn, recompense them for their deeds and assign them their destinations [i.e. hell or paradise].
[An Excerpt from ‘Tayseer al-Kareem Ar-Rahmaan Fee Tafseer Kalaam al-Mannaan’. Slightly paraphrased]