Shaykh al-Islam Ibn Taymiyyah (may Allah have mercy on him) said:
A beneficial principle concerning: the obligation of adhering to the divine message; the fact that all happiness and guidance is in following the Messenger (peace be upon him), and that misery and misguidance is in opposing him; the fact that the origin of every good in existence, whether general or specific, is from the Messenger (peace be upon him); the fact that the reason for every evil in the world relating specifically to the individual is his opposition of the Messenger (peace be upon him), or ignorance of what he brought; and that people’s happiness in their present life and next life is by following the divine message.
Having a divine message is necessary for people; they must have it. Their need for it is above their need for everything else. Moreover, the divine message is the spirit, life and light of the world. So what good is there for the world if its spirit, life and light are missing? Also, the life of this world is dark and cursed, except for what the sun of the divine message rises over. The same with the individual; so long as the sun of the divine message does not emanate in his heart, acquiring of its spirit and life, he is in darkness and is counted from among the dead. Allah Almighty says:
“And is one who was dead and We gave him life and made for him light by which to walk among the people, like one who is in darkness, never to emerge therefrom?” [Al-An`am 6:122]
So this is the description of the believer; he was dead in the darkness of ignorance, then Allah gave him life through the spirit of the divine message and the light of Iman, and made for him light by which to walk among the people. As for the disbeliever, then he is one whose heart is dead in darkness.
Furthermore, Allah Almighty has referred to His message as a spirit; and if the spirit is missing, there is no life. Allah Almighty says:
“And thus We have revealed to you a spirit (inspiration) of Our command. You did not know what the Book or Iman was, but We have made it a light by which We guide whom We will of Our slaves.” [Al-Shura 42:52]
So He mentioned the two sources here, which are: the spirit and light. The spirit is life and the light is light [of guidance].
[Majmu` al-Fatawa (19/93-94)]
ضرورة الناس للرسالة والشريعة.