Pope Francis urged Catholics to ask Christ for the "gift of mercy" in a letter marking the 90th anniversary of the first appearance of Jesus to St. Faustina Kowalska on Monday.

In a letter to Bishop Piotr Libera of Płock, the pope noted that the first apparition took place on Feb. 22, 1931.

"Let us ask Christ for the gift of mercy. Let it engulf us and penetrate us. Let us have the courage to come back to Jesus to meet His love and mercy in the sacraments," he said in the letter, dated Feb. 15.

"Let us feel His closeness and tenderness, and then we will also be more capable of mercy, patience, forgiveness, and love."

St. Faustina recorded the apparition, which took place in Płock, in her diary. The Polish nun said that Jesus appeared to her dressed in white, with two rays emerging from his chest, one red and the other pale. She reported that Christ asked her to create an image of him bearing the words "Jesus, I trust in you."

She wrote that Jesus said: "I desire that this image be venerated, first in your chapel, and [then] throughout the world." 

The image was first painted by the Polish artist Eugeniusz Kazimirowski. After the nun's death in 1938, other artists created images inspired by her description of the apparition. The best-known version was painted by the Polish painter Adolf Hyła for the Sanctuary of Divine Mercy in 1943. 

St. Faustina was canonized by Pope John Paul II in the year 2000, becoming the first saint of the new millennium. 

Pope Francis said that he united himself in prayer with those taking part in a solemn celebration of the 90th anniversary at the Sanctuary of Divine Mercy in Łagiewniki.

He wrote: "I would like to recall the words of the Lord Jesus recorded by the saint in her Diary: 'Humanity will not know peace until it turns to the source of my mercy.'" 

He recalled that St. John Paul II, "the Apostle of Mercy," wanted the message of God's merciful love to reach all the world's inhabitants. 

Quoting an address that his predecessor gave in Łagiewniki in 2002, Pope Francis said: "This fire of mercy needs to be passed on to the world. In the mercy of God, the world will find peace and mankind will find happiness!"

The pope also referred to the 90th anniversary after reciting the Angelus on Sunday.

He said: "Today my thoughts go to the Shrine of Płock in Poland, where 90 years ago the Lord Jesus manifested Himself to St. Faustina Kowalska, entrusting a special message of divine mercy to her." 

"Through St. John Paul II this message reached the entire world, and it is none other than the Gospel of Jesus Christ, who died and rose again, and who gives us His Father's mercy. Let us open our heart, saying with faith, 'Jesus, I trust in You.'"