VATICAN CITY (CNS) — Many challenges in Japan make the church’s evangelizing call to be the “salt and light” of hope and meaning even more urgent than ever, Pope Francis told the country’s bishops.

In fact, the nation’s long history of courageous martyrs represents “the true evangelizing power of your church,” he said, and they are a great treasure that should always be remembered, cherished and built upon.

The pope’s remarks came in a letter, addressed to all bishops in Japan, that was to be delivered by Cardinal Fernando Filoni, prefect of the Congregation for the Evangelization of Peoples, who was visiting Japan Sept. 17-26.

Some of the many worrying problems the country faces include high divorce rates, suicide, religious indifference and an “obsession for work and earnings,” the pope said in the letter dated Sept. 14, the feast of the Exaltation of the Holy Cross.

A highly developed nation can produce material wealth, but also material, spiritual and moral poverty and exclusion, he wrote.

That is why it is urgent the church in Japan constantly “be salt and light” in the world, he said.

Like real salt, he said, the church must prevent “decay and give flavor,” and like light, “keep darkness from prevailing.”

Like the tiny mustard seed, the minority Catholic Church in Japan has been entrusted with a great mission, and the lack of priests and religious there must never impede the call to evangelize, he said. Rather, it should inspire them to tirelessly seek new workers for the Lord’s vineyard.