Every person knows that certitude (Yaqeen) is a function of the heart, which is known through intuition. For e.g., there is a certain (poisonous) herb, on eating which anybody would die. In the beginning, one will have one’s doubts about it. Then if some 10, 20 people eat that herb and all die in front of this person, then that doubt will be dispelled and a certain feeling will be developed in one’s heart due to which neither will that person eat that herb himself nor allow anyone else to eat it. If at all he allows someone to eat it, it will be those whom he desires to be dead.
This is the feeling about the effect of that herb. If one has to attain such a feeling about sensory objects, one do so by experiencing them and that is in their power. However, if one wants to have such a feeling about things which are above the senses, then it is not in the power of human beings, because the intellect searches for such answers which stop this feeling from developing. That’s the reason why many people don’t believe in Allah Most High. They have reduced the world to matter and atoms and such. As per them, whatever is created is created because of the changes in matter. Even though many proofs are given to refute them, still their minds hammer out “answers” for those proofs as well.
Thus, intellects are unable to gain certitude about non-sensory things. As long as that certitude is not cast into the heart by Allah Most High, it cannot be gained. For this reason, Allah Most High says:
Is he whose bosom Allah Most High has enlightened for Islam so that he follows a light from his Lord…..Surah Zumar (39:22)
After this the intellect also develops proofs in support of this. Then there are various stages of that enlightenment of the bosom. It is not possible that the enlightenment of the populace should be like the enlightenment of the Prophets (May peace be upon him). See, the certitude which the Prophets (May peace be upon him) and the saints have on Allah Most High, His attributes, His signs, it has such effect that the certitude of the common people doesn’t have that effect, even though a person with such weak certitude will also be considered a Muslim.
However, due to their weak certitude, acts which go against the will and wish of Almighty Allah will be committed by such persons, which make them liable to be punished. On the other hand, those with absolute certitude are as if seeing Allah Most High and His attributes, His rewards and punishments all the time, which makes acting against the will and wish of Allah Most High well nigh impossible or (at least) highly difficult.
In Islam this status is really lofty and is sought for its own sake (Maqsood bidh Dhaat). The manner of achieving it is to worship Allah Most High as much as possible. The Arabic word for worship (Ibaadat) means humility and debasement and debasement (the Arabic word for it) means to be obedient.
When a person expresses (his or her) humility before Allah Most High and becomes obedient to Him in deeds and beliefs, then there are high hopes that in lieu of that Allah Most High will grant that certitude, which makes it impossible to commit deeds which are against the will of Allah Most High. The words of Allah Most High:
And worship Your Lord until You attain the station of certitude (as it befits You)..Surah Hijr (15:99)
The Holy Prophet (Sallallahu alaihi wa sallam) has ordered this in the Hadith of Ihsaan.