Immense faith and sincerity.

One must have tremendous faith in religion and God. Until one has it, one cannot aspire to be a Jnâni. A great sage once told me that not one in twenty millions in this world believed in God. I asked him why, and he told me, “Suppose there is a thief in this room, and he gets to know that there is a mass of gold in the next room, and only a very thin partition between the two rooms; what will be the condition of that thief?” I answered, “He will not be able to sleep at all; his brain will be actively thinking of some means of getting at the gold, and he will think of nothing else.” Then he replied, “Do you believe that a man could believe in God and not go mad to get him? If a man sincerely believes that there is that immense, infinite mine of Bliss, and that It can be reached, would not that man go mad in his struggle to reach it ?” Strong faith in God and the consequent eagerness to reach Him constitute Shraddha.

Swami Vivekananda
(The Complete Works of Swami Vivekananda/Volume 1/Lectures And Discourses/Steps To Realisation)