It will not benefit the one who says it unless the following seven conditions are fulfilled(1):-
Firstly: Knowledge (al-’ilm) of its meaning, what it negates and affirms. If a person says it without knowing its meaning, nor what its requirements are, then he will not benefit by it, because he has not believed in what it requires. Rather, he is like someone who speaks in a language that he does not understand.
Secondly: Certainty (al-yaqeen), which is [to have] complete surety of it and which leads to repelling any doubt or suspicion about it.
Thirdly: Exclusively worshipping Allaah (al-ikhlaas), which is contrary to shirk. This is what laa ilaaha illallaah points towards.
Fourthly: Truthfulness (as-sidq), which prevents hypocrisy (nifaaq). Indeed, the hypocrites uttered it with their tongues, but did not inwardly believe in what it signified.
Fifthly: Love (al-mahabbah) for this kalimah and having love and pleasure for whatever it necessitates. This is contrary to the [state of the] hypocrites.
Sixthly: Submissive compliance (al-inqiyaad), by fulfilling its rights - which are the obligatory actions - with sincerity to Allaah and seeking His good pleasure. This is its requirement.
Seventhly: Acceptance (al-qabool), which prevents rejection. This is achieved by acting upon what Allaah has commanded and abandoning whatever He has prohibited. Scholars have deduced these conditions from those texts of the Book and the Sunnah which are pertinent to [understanding] this great kalimah; and which explain its rights and restrictions and that it is not merely a word that a person utters.
1) Some scholars, such as Shaykh ‘Abdul-’Azeez bin Baaz in Majmoo’ Fataawaa wa Maqaalaat Mutanawwi’ah (7/56) and Shaykh ‘Abdullaah ibn Jibreen in ash-Shahaadataan (p.77), add an eighth condition: The rejection of whatever else is worshiped besides Allaah.