Likewise, it is the key to the path to Allāh the Exalted, and the foundation of His Laws [Sharīʿah]. So the messengers were united upon calling to it. Allāh the Exalted says:

وَمَا أَرْسَلْنَا مِن قَبْلِكَ مِن رَّسُولٍ إِلَّا نُوحِي إِلَيْهِ أَنَّهُ لَا إِلَٰهَ إِلَّا أَنَا فَاعْبُدُونِ ‎﴿٢٥﴾‏

“And We did not send before you any messenger, except that We revealed to him that there is none worthy of worship except Me, so worship Me.”
[al-Anbiyāʾ, 21:25]

Allāh Himself testifies to His Oneness, and the angels, and the people of knowledge testify to it also. Allāh the Exalted said:

شَهِدَ اللَّهُ أَنَّهُ لَا إِلَٰهَ إِلَّا هُوَ وَالْمَلَائِكَةُ وَأُولُو الْعِلْمِ قَائِمًا بِالْقِسْطِ ۚ لَا إِلَٰهَ إِلَّا هُوَ الْعَزِيزُ الْحَكِيمُ ‎﴿١٨﴾‏

“Allāh the Exalted testifies that there is none worthy of worship except Him, and so do the angels, and those of knowledge – [that He is] maintaining [creation] in justice. There is none worthy of worship except Him, the Exalted, the Mighty, the Wise.”
[Āli ʿImrān, 3:18]

Since this is the nature of tawḥīd, it is binding upon every Muslim to devote himself to learning, teaching, contemplating on, and believing in it, so that his religion may be built upon safe foundations, and so that he may be satisfied, and get the blessings of its fruits and results.¹

The Religion of Islām

The Religion of Islām is the religion which Allāh sent Muḥammad (ﷺ) with. Allāh abrogated with it all other religions, and perfected it for His slaves, and completed with it His favour upon them, and chose it for them as a religion. So no religion besides it will be accepted. Allāh the Exalted said:

مَّا كَانَ مُحَمَّدٌ أَبَا أَحَدٍ مِّن رِّجَالِكُمْ وَلَٰكِن رَّسُولَ اللَّهِ وَخَاتَمَ النَّبِيِّينَ ۗ ‎﴿٤٠﴾‏

“Muḥammad is not a father from any of your men, rather he is the Messenger of Allāh, and the last of the prophets.”
[al-Aḥzāb, 33:40]

And Allāh the Exalted said,

 الْيَوْمَ أَكْمَلْتُ لَكُمْ دِينَكُمْ وَأَتْمَمْتُ عَلَيْكُمْ نِعْمَتِي وَرَضِيتُ لَكُمُ الْإِسْلَامَ دِينًا ۚ‎﴿٣﴾‏

“Today I have perfected for you your Religion, and completed for you My favour upon you, and have chosen for you Islām as a religion.”
[al-Māʿidah, 5:3]

And Allāh the Exalted said:

إِنَّ الدِّينَ عِندَ اللَّهِ الْإِسْلَامُ ۗ ‎﴿١٩﴾

“Verily the religion with Allāh is Islām.”
[Āli ʿImrān, 3:19]

 And Allāh the Exalted said,

وَمَن يَبْتَغِ غَيْرَ الْإِسْلَامِ دِينًا فَلَن يُقْبَلَ مِنْهُ وَهُوَ فِي الْآخِرَةِ مِنَ الْخَاسِرِينَ ‎﴿٨٥﴾

“And whoever takes other than Islām as a religion, it will never be accepted from him, and he will be in the Hereafter – from the losers.”
[Āli ʿImrān, 3:85]

Indeed Allāh made obligatory upon all the people to specify worship for Him. So He said in speaking to the Messenger (ﷺ):

قُلْ يَا أَيُّهَا النَّاسُ إِنِّي رَسُولُ اللَّهِ إِلَيْكُمْ جَمِيعًا الَّذِي لَهُ مُلْكُ السَّمَاوَاتِ وَالْأَرْضِ ۖ لَا إِلَٰهَ إِلَّا هُوَ يُحْيِي وَيُمِيتُ ۖ فَآمِنُوا بِاللَّهِ وَرَسُولِهِ النَّبِيِّ الْأُمِّيِّ الَّذِي يُؤْمِنُ بِاللَّهِ وَكَلِمَاتِهِ وَاتَّبِعُوهُ لَعَلَّكُمْ تَهْتَدُونَ ‎﴿١٥٨﴾

“Say: ‘O mankind, indeed I am the Messenger of Allāh to you all, [To Him] belongs the dominion of the heavens and the earth. There is none worthy of worship except Him; He gives life and causes death.’ So believe in Allāh and His messenger, the unlettered prophet, who believes in Allāh and His Words, and follow Him so that you may be guided.”
[al-Aʿarāf, 7:158]

In Ṣaḥīḥ Muslim from Abī Hurayrah (raḍī Allāhu ʿanhu), from the Messenger of Allāh (ﷺ) that he said: “By Him in whose Hand is the soul of Muḥammad, no one is from the Jews or the Christians, and then he dies and he has not believed in that which I was sent with, except that he is from the people of the Fire.”²

To believe in Islām means to believe in what he (ﷺ) brought with approval and submission, not mere belief. Consequently, Abū Ṭālib was not a believer in the Messenger (ﷺ), along with what he came with, even though he testified that it was the best of religions.

The religion of Islām has guaranteed all the good things that were included in the previous religions. It is distinguished because its good is valid in all times and places, and peoples. Allāh the Exalted says in speaking to His Messenger (ﷺ):

وَأَنزَلْنَا إِلَيْكَ الْكِتَابَ بِالْحَقِّ مُصَدِّقًا لِّمَا بَيْنَ يَدَيْهِ مِنَ الْكِتَابِ وَمُهَيْمِنًا عَلَيْهِ ۖ ‎﴿٤٨﴾‏

“And We revealed to you the Book in truth, affirming what preceded it from the books, and a supervisor over them.”
[al-Māʿidah, 5:48]

This means that its existence is good for all times places and people. Following it does not negate the benefit of a nation in any time or place, rather it benefits them. This does not mean that it is subject to every time place or people as some of the people think.

The religion of Islām is the true religion through which Allāh guarantees the one who adheres to it with His Help, and He will render him victorious over all others. Allāh the Exalted says:

هُوَ الَّذِي أَرْسَلَ رَسُولَهُ بِالْهُدَىٰ وَدِينِ الْحَقِّ لِيُظْهِرَهُ عَلَى الدِّينِ كُلِّهِ وَلَوْ كَرِهَ الْمُشْرِكُونَ ‎﴿٩﴾

“He is the one who sent His Messenger with the true Religion, to render it victorious over all other Religions, even though the idolaters may detest it.”
[al-Ṣaff, 61:9]

Allāh the Exalted says:

وَعَدَ اللَّهُ الَّذِينَ آمَنُوا مِنكُمْ وَعَمِلُوا الصَّالِحَاتِ لَيَسْتَخْلِفَنَّهُمْ فِي الْأَرْضِ كَمَا اسْتَخْلَفَ الَّذِينَ مِن قَبْلِهِمْ وَلَيُمَكِّنَنَّ لَهُمْ دِينَهُمُ الَّذِي ارْتَضَىٰ لَهُمْ وَلَيُبَدِّلَنَّهُم مِّن بَعْدِ خَوْفِهِمْ أَمْنًا ۚ يَعْبُدُونَنِي لَا يُشْرِكُونَ بِي شَيْئًا ۚ وَمَن كَفَرَ بَعْدَ ذَٰلِكَ فَأُولَٰئِكَ هُمُ الْفَاسِقُونَ ‎﴿٥٥﴾‏

“Allāh has promised those among you who have believed and done righteous deeds, that He will surely grant them succession [to authority] upon the earth just as He granted it to those before them and that He will surely establish for them their Religion, which He has preferred for them and that He will surely substitute for them, after their fear, security. They worship Me, not associating anything with Me. But whoever disbelieves after that; then they are the disobedient ones.”
[al-Nūr, 24:55]

The religion of Islām is a creed and a law, so it is perfect in its belief and law:

1. It commands the Oneness of Allāh, and it forbids from shirk [associating partners with Allāh].
2. It commands truthfulness and forbids from lying.
3. It commands justice,³ and forbids from oppression.
4. It commands truthfulness and forbids from treachery.
5. It commands the keeping of promises and it forbids from treason.
6. It commands righteousness towards parents and forbids from disobedience to them.
7. It commands the keeping of the ties of kinship – and they are the family – and it forbids from cutting oneself off from them.

The comprehensive statement is that Islām commands with all virtuous characteristics, and that it forbids from every despicable characteristic. It commands every good action, and it forbids from every sinful action. Allāh the Exalted said:

إِنَّ اللَّهَ يَأْمُرُ بِالْعَدْلِ وَالْإِحْسَانِ وَإِيتَاءِ ذِي الْقُرْبَىٰ وَيَنْهَىٰ عَنِ الْفَحْشَاءِ وَالْمُنكَرِ وَالْبَغْيِ ۚ يَعِظُكُمْ لَعَلَّكُمْ تَذَكَّرُونَ ‎﴿٩٠﴾

“Verily Allāh commands with justice and good conduct to relatives, and forbids immorality and bad conduct and oppression. He admonishes you that perhaps you will be reminded.”
[al-Naḥl, 16:90]⁴

So verily the knowledge of tawḥīd [the oneness of Allāh] is the noblest of sciences, and the greatest in rank, and most obligatory to be studied because it is the knowledge of Allāh the Exalted, and His Names, and His Attributes, and His Rights upon His slaves.