Pope Francis officially has declared St. Irenaeus of Lyon a doctor of the church.

In a decree released by the Vatican Jan. 21, the pope ordered that the second-century theologian be given the title of "doctor of unity" and said St. Irenaeus' life and teachings served as "a spiritual and theological bridge between Eastern and Western Christians."

"May the doctrine of such a great teacher increasingly encourage the journey of all the Lord's disciples toward full communion," the pope said.

During a meeting with Pope Francis Jan. 20, Cardinal Marcello Semeraro, prefect of the Congregation for Saints' Causes, asked the pope to "accept the affirmative opinion" of the cardinals and bishops who are congregation members to confer the title on St. Irenaeus, who was known for his defense of orthodoxy amid the rise of gnostic sects.

St. Irenaeus is the second doctor of the church named by Pope Francis after St. Gregory of Narek, who was given the designation in 2015. He brings the total number of doctors of the church to 37.

Born in Smyrna, Asia Minor -- now modern-day Turkey -- St. Irenaeus was known as a staunch defender of the faith.

Concerned about the rise of gnostic sects within the early Christian church, he wrote "Adversus haereses" ("Against Heresies"), a refutation of gnostic beliefs that emphasized personal spiritual knowledge over faith in Christian teachings and in ecclesiastical authority.

In October, the pope had told members of the St. Irenaeus Joint Orthodox-Catholic Working Group that he intended to declare their namesake a doctor of the church.

"Your patron, St. Irenaeus of Lyon -- whom I will soon declare a doctor of the church with the title, 'doctor unitatis' ('doctor of unity') -- came from the East, exercised his episcopal ministry in the West, and was a great spiritual and theological bridge between Eastern and Western Christians," he said.

During his meeting with Cardinal Semeraro, Pope Francis also signed decrees recognizing how three sainthood candidates -- one man and two women -- heroically lived the Christian virtues. The three were:

-- Italian Archbishop Francesco Saverio Toppi, the former prelate of Pompei, who was known for his devotion to Our Lady of the Most Holy Rosary. He was born in 1925 and died in 2007.

-- Italian Sister Maria Teresa De Vincenti, founder of the Little Workers of the Sacred Heart. She was born in 1872 and died in 1936.

-- Italian Sister Gabriella Borgarino, a member of the Daughters of Charity. She was born in 1880 and died in 1949.