You’ve probably noticed that the teachings by the Buddha all start off in a very similar way.  For instance, the Diamond Sutra starts off with:

Thus have I heard.  At one time, the Buddha was in the city of Sravasti at the Jeta Grove Monastery with a gathering of monks numbering 1,250.

Here’s how each teaching, or sutra, starts off with the six required conditions:

  1. Thus  –  Faith:  The faith of the assembly must be established in order to hear the teaching
  2. have I heardListening:  those assembled must have the necessary merit to hear the teachings
  3. at one time  –  Time:  the time to hear the teachings have ripened (the exact time is never given on purpose to eliminate the limited concept of time and space that living beings have)
  4. the Buddha  –  Teacher:  the master delivering the Dharma
  5. city of Sravasti at the Jeta Grove  –  Location:  The venue that the teachings are being given in is determined to be acceptable
  6. gathering of monks numbering 1,250  –  Audience:  the faithful assembled are ready to hear the teachings of the dharma

These six conditions must be present in order for a Dharma teaching to occur.  The only exception is the Eight Realizations of a Bodhisattva Sutra where “Thus have I heard…” is not included because the Parthian monk, An Shigao, more than likely decided not to include the introductory passage so the sutra would be more accessible to his Chinese audience.

For more information, refer to the two books by Ven. Master Hsing Yun:  Four Insights for Finding Fulfillment and The Great Realizations.