Thanks, Seng Kiat, for the explanation.
Here is another post that discusses that issue: “Four Conditions for Attaining Sōtapanna Magga/Phala”
The main points are the following:
1. The “Ministry of the Buddha” or the “Buddha Sāsana” with the unique message of the Buddha will last only as long as there are Noble Persons (those who have attained magga phala, i.e., Sotapanna through Arahant) stages.
– They have the special name “kalyāṇa mittā” of a “Noble friend.”
2. Only a Buddha or a true disciple of the Buddha (who has grasped the teachings of the Buddha) can explain those teachings.
– Once there is no longer any such kalyāṇa mittā on the Earth, Buddha Sāsana will disappear.
– Then, the world will have to wait for the next Buddha, Buddha Maitreya, to be born to attain magga phala (Nibbana.) That is supposed to happen in a billion years or so.
– The current Buddha Sāsana of Buddha Gotama is expected to disappear within the next 2000 years.
P.S. That is why the Buddha told Ven. Ananda (in the Upaḍḍha Sutta (SN 45.2)) that the continuation of his Buddha Sāsana depends TOTALLY on kalyāṇa mittā.