When a man embraces the faith, he makes a sincere vow. Thereafter, different practical occasions arise in life when he is required to act according to his vow. Now, one who, on such occasions, hears the voice of his heart and fulfils the requirements of his vow, has in effect revived and confirmed his vow of faith. On the contrary, one who hears his inner voice, ignores it and acts in breach of his vow, will gradually become less and less conscious of his vow and will eventually become completely insensitive about his vow of faith. This, in fact, is the meaning of ‘their hearts are sealed up’.