Ibn al-Qayyim said, explaining how people need the Messengers and their teachings: “Hence we know that above all else, people need to know about the Messenger and the message he brought, to believe what he told us and to believe what he told us and to obey what he enjoined upon us, because there is now way to attain happiness and success, either in this world or in the hereafter, except at the hands of the Messengers.
There is no way to know about good and evil in detail except through them. No can attain the pleasure of Allah at all except through following their teachings. Good words, deeds and attitudes can only be attained through their guidance and the teachings they brought. They are the standard example: attitudes, manners and actions are to be measured against their words and attitudes. Following them makes the people of misguidance stand out. So our need for them is greater than 's the body's need for the soul, or the need of the eye for light, or the soul's need for its life. Whatever need or necessity you may think of, a person's need for the Messenger is many times greater.
What do you think of the importance of a Prophet who, if his guidance goes away from you even for an instant, your heart will be corrupted, and you will be like a fish taken out of the water and placed in the frying pan? This is the state of the man who deviates from the way of the Messenger. Indeed he is much worse off, but no one realises this except one in whose heart is life, for the dead person does not feel the pain of a wound. Because a person's happiness in this world and the hereafter is connected to the guidance of the Prophet (peace be upon him), then each person who is sincere with himself and who wants to attain salvation and happiness had to know enough about his (the Prophet's) teachings, biography and way to ensure he is not one of those who are ignorant of him so that he be included among his followers and his party.
People vary with regard to this: some follow a little, some follow a lot and some are deprived completely. Bounty is in the hand of Allah; he gives to whomsoever he wills, and Allah is the owner of great bounty."
Source: Al-Ashqar, Umar S., The Messengers and the Messages, IIPH, Riyadh, Saudi Arabia, 2003, p. 55-56.