She was a woman of faith, Catholic by conviction and not simply by education, who lived her Credo in act and in truth, in discretion. She said, one day, that for her, faith was a sublimated doubt, namely, a doubt purified to the point of becoming a conviction, which alone can give meaning to the life of human beings. Therefore, she placed her trust in the Lord's Providence, and served His Church without ostentation. She was wary, however, of the expression "Christian charity", preferring to practice charity simply. At times, she could be rather intolerant of believers who lived their faith in a different way. She confessed that she did not understand the Charismatic movement and acknowledged her mistrust of excessive manifestations of faith, considering them, in the extreme, to be religious deviations. Finally, she did not hesitate to declare herself firmly opposed to all fundamentalism, manifesting, in this way, her sense of the just measure, and her horror of fanaticisms.Here is an excerpt from Lilian's Will, also suggesting a sober, thoughtful piety. People tend to associate Lilian's flamboyant glamor with worldliness, but there is no reason why a lover of beauty cannot also love God. In fact, the idealism and perfectionism inherent in her love of beauty might actually have led her to the love of God.
Lilian's husband, King Léopold III, was also a person of profound faith. Joseph E. Davies, an American ambassador to Brussels, once described Léopold as "a noble man and a very great Christian gentleman", although few might think it today, and according to the King's biographer Georges-Henri Dumont, one of the traits that attracted Léopold to Lilian was the strong religious faith they shared.