VATICAN CITY (CNS) -- The "small yet vibrant church" in Estonia has been a source of compassion and spiritual sustenance for countless people in the Baltic nation, Pope Francis said.

"Even the tiniest of plants, the smallest of gestures and the lowliest of offerings can grow far beyond their humble beginnings to bestow a rich harvest," he said in a letter sent to Bishop Philippe Jourdan of Tallinn, Estonia. The Vatican published a copy of the letter Nov. 3.

The pope sent his "heartfelt greetings, together with the assurance of my spiritual closeness," to the bishop and the entire Catholic community on the occasion of the 100th anniversary of the creation of the apostolic administration of Estonia, which the pope elevated to a diocese Sept. 26.

According to Vatican statistics, less than half of 1 percent of Estonia's population is Catholic.

Pope Francis visited Estonia and its Baltic neighbors, Latvia and Lithuania, in 2018, the year the three nations celebrated the 100th anniversary of their declarations of independence after World War I. While declared Soviet republics in 1940, the countries were occupied by the Nazis during World War II and then lived under Soviet rule from 1944 to 1990. Today they are members of the European Union.

In his letter to Bishop Jourdan, the pope said that the anniversary "marks a century of steadfast fidelity to the Catholic faith, which has enabled this small yet vibrant Church to be a source of compassion and spiritual nourishment for countless men and women across the nation."

"At the same time, this anniversary commemorates unwavering hope and trust in the Lord through decades of suffering, occupation and oppression," he added.

Pope Francis said he hoped Catholics in Estonia would continue to "seek to build a society rooted in peace, justice, solidarity and the dignity of every human person" and to do so by working more with other Christian denominations "in bearing a united witness to God's promises."

"This is especially important in the context of today's war in Europe, which is a source of deep anxiety and tragically echoes the darker moments of yesteryears," he wrote.

He urged all Christians, "together with people of goodwill, to extend the hand of friendship to refugees and the most vulnerable of our brothers and sisters."