“A person should know and realize that the Creator, may He be exalted, is watching him, and nothing is hidden from Him; neither his outer nor his inner life, neither his outer appearances nor his inner convictions.  And He knows whether a person’s trust in Him is sincere or not.  As it says in Scripture: ‘G-d knows the thoughts of man, that they are in vain’ (Tehillim 94:11); ‘Will not He, Who appraises the heart, discern?’ (Mishlei 24:12); ‘For You alone know the hearts of all men’ (Melachim I, 8:39).

When this is clear to a person, it is improper for him to profess in his speech that he trusts in G-d if he does not trust in Him in his heart and inner self.  For then he would be on the level of those of whom it is said: ‘With their mouth and with their lips they honor Me, while their heart they keep far from Me.’ (Yeshayahu)” ~ Chovos Halevos