Wahb ibn Munnabih was asked:
"Isn’t La Ilaha Ila Allah the key to Jannah?" 
He responded: "But of course, but there is not a key except that it has ridges, so if you come with a key that has ridges, [the door] would be opened for you, otherwise it would not be opened."
Meaning that simply saying the statement of Tawheed, without what it necessitates, without its conditions, is like a key without ridges (an uncut key), and only a key with ridges (i.e. is cut) can open something.
 On the authority of Mu'aadh ibn Jabal who said; the Messenger of Allaah said:
"The key to Jannah is the proclamation of 'Laa Ilaaha Illa Allah'."
[Collected by al-Imaam Ahmad in his Musnad.]