The Prophet (peace be upon him) said: &"Islam is built on five (pillars): The testimony that there is none worthy of worship but Allah, establishing Salah, giving Zakah, Hajj, and fasting Ramadan&" (Narrated by Al-Bukhari)&"La ilaha illallah&" for its sake Allah beautified Jannah and He created Jahanem, and for its sake the scale of good and evil deeds will be set up.
Furthermore he (peace be upon him) said: &"The best of what I and the Prophet before me have said is: &"None has the right to be worshipped but Allah, Alone. He has no partner, to Him belongs all that exists, and to Him belongs the Praise, and He is over all things (in His power).&" (La ilaha illallah, wahdahu la sharika Lahu, Lahul-Mulku wa Lahul-Hamdu, wa Huwa ala kulli shai’in qadir)’” (Narrated by At-Tirmidthi)
He (peace be upon him) also said: “When prophet Nuh was dying, he told his son: ‘I will give you some instructions. I will command you to do two things and I will forbid you from doing two things. I command you to say: “There is no god but Allah.” If the seven heavens and the seven earths were a dark ring, they would be broken to pieces by this phrase: &"There is no god but Allah&"&"(Narrated by Al-Bukhari in “Al-Adab Al-Mufrad”)
1-Knowing its meaning: The person uttering this statement should know its meaning and that it negates any divinity other than that which is ascribed to Allah. Allah the Exalted says: “So know (O Muhammad) that there is no deity but Allah…&" (Muhammad or Al-Qitâl: 19).
2-Certitude: This means that no doubt enters the heart of he who utters this statement with regards to its meaning and also what it contains and what it implies. Allah says: &"The believers are only the ones who have believed in Allah and His Messenger and then doubt not but strive with their properties and their lives in the cause of Allah. It is those who are the truthful&" (Al-Hujurât: 15).
The Prophet (peace be upon him) said: &"I bear testimony to the fact that there is no god but Allah, and I am His messenger. The bondsman who meets Allah without entertaining any doubt about these (two fundamentals) will enter heaven&" (Narrated by Muslim)
3-Accepting what this statement requires with the heart and the tongue: What is meant by that acceptance is the complete opposite of turning a deaf ear or of being arrogant. Allah (mighty and majestic is He) says: 34- Indeed, that is how We deal with the criminals. 35- Indeed they, when it was said to them: &"There is no deity but Allah,&" were arrogant (As-Sâffât: 34-35).Slavery -in fact- is a state of the heart, for a person becomes a slave to whatever or whoever enslaves and controls his heart.
4-Acting on what this statement indicates: This means that the slave of Allah carries out Allah&"s commands and abstains from what He forbids. Allah says: &"And whosoever submits his face to Allah while he is a doer of good - then he has grasped the most trustworthy handhold; and to Allah will be the outcome of (all) matters&" (Luqmân: 22).
5-Honesty: This means that the person says this statement truthfully from his heart, and his tongue utters it truthfully too. Almighty Allah says: 8- And of the people are some who say: &"We believe in Allah and the Last Day,&" but they are not believers. 9- They (think to) deceive Allah and those who believe, but they deceive not except themselves and perceive (it) not (Al-Baqarah: 8-9).
6-Sincerity: This is to utter this statement only for the sake of gaining Allah’s Pleasure, and not for any other reason. Allah says: &"And they were not commanded except to worship Allah, (being) sincere to Him in religion and inclining to truth, and to establish prayer and to give zakah. And that is the correct religion&" (Al-Baiyinah: 5).
7-To love this statement of His Oneness, those who utter it, act upon it and who adhere to its conditions, and to hate those who nullify it. Allah (mighty and majestic is He) says: &"And (yet), among the people are those who take other than Allah as equals (to Him). They love them as they (should) love Allah, but those who believe are stronger in love for Allah&" (Al-Baqarah: 165).The more the heart loves Allah, the more enslaved it is to Him and free of enslavement of any other thing or being.
This is &"La illaha illallah&" and these are its conditions with which a person reaches a high status with Allah (mighty and majestic is He). It was said to Al-Hassan Al-Basry: &"Some say: &"He who says &"La Illaha Illallah&" enters Jannah.&" He replied: &"Who says La Illaha Illallah and gives that statement its right and fulfills what it implies, then he will enter Jannah.&"&"
&"La illah illallah&" only benefits the person who utters it when he puts it into practice and fulfills its conditions. As he who utters it and fails to practice it, he does not benefit anything from uttering it.