The Bible says, "The Kingdom of Heaven is like a treasure hidden in the field, which a man found and hid again; and from joy over it he goes and sells all that he has and buys that field. Again, the Kingdom of Heaven is like a merchant seeking fine pearls, and upon finding one pearl of great value, he went and sold all that he had and bought it” (Matt 13:44-46 NASU).
They gave up everything for the treasure they had found! How do we know they believed? Their actions confirmed it.