5 The heart is also the locus of sincerity, where deceit and disguise have no place. It usually indicates our true intentions, what we really think, believe and desire, the “secrets” that we tell no one: in a word, the naked truth about ourselves. It is the part of us that is neither appearance or illusion, but is instead authentic, real, entirely “who we are”. That is why Samson, who kept from Delilah the secret of his strength, was asked by her, “How can you say, ‘I love you’, when your heart is not with me?” ( Judg 16:15). Only when Samson opened his heart to her, did she realize “that he had told her his whole secret” ( Judg 16:18).
Source: Dilexit Nos (Vatican.va)