Frequently the Buddha will not respond until he has been asked the same question three times or until he has been assured of some thing three different times. This repetition is an indication of the significance of a certain thing. It is a test of sincerity. It is a test of commitment. It is not intended to be viewed as being cruel or teasing. Three times is almost as if a seal has been made or a serious vow has been offered.
Lecture on the Lotus Sutra