I found the answer. The power of Arahants are so sublime. They were able to see a future era and the future of the Sasana. This is from chapter 5 of the Mahavamsa:
At the time of the Second Council, the elders looked into the future and saw that during King Asoka’s reign a danger would arise for the Dispensation. Looking throughout the whole world for one who could remove that danger, they saw the Brahmā Tissa, whose remaining lifespan was short.
They approached that great being and requested him:
“Please be reborn among humans and remove this danger to the Dispensation.”
Wishing to illuminate the Dispensation, he gave them his promise.
Then the elders spoke to the young monks Siggava and Caṇḍavajji:
“More than one hundred and eighteen years from now, danger will arise for the Dispensation. We will not still be alive then. You two did not attend this legal matter of the Saṅgha, and therefore you are liable to a disciplinary penalty (daṇḍakamma). This shall be your penalty: for the purpose of illuminating the Dispensation, the great Brahmā Tissa will be conceived in the house of the brahmin Moggali. When the time comes, one of you must ordain that boy, and the other must teach him the Buddha’s word thoroughly.”
Phussattheragāthā also shows that an Arahant can see the future of the world through knowledge of the future (anāgataṃsa-ñāṇa)
Excerpt:
Then, using knowledge of the future (anāgataṃsa-ñāṇa), Phussa Thera saw the future conduct of monks and nuns exactly as it would occur and described it.
The verses beginning:
“They will be angry and resentful…”
and ending:
“Develop the Noble Eightfold Path and realize the Deathless”
are his prophetic description of the future decline of discipline and his exhortation to practice heedfulness (appamāda).