Every Sunday during Mass, just after the Gospel reading, Catholics stand and in unison recite the Nicene Creed. Dating back to the First Council of Nicaea in the summer of A.D. 325, this classic profession of faith was developed in response to the Arian heresy. For the first time, the faithful had a succinct list of core teachings which the Church held to be true.

And the guy to thank for its inclusion in the Mass is the sixth-century bishop of Seville, St. Leander – whose feast we celebrate on March 13.


Who Was St. Leander?

Leander was born in Carthago Nova (present-day Cartagena), on the southern coast of Spain's Iberian Peninsula, around the year 534. When he was in his late teens, his father Severianus moved the family to Seville. 

His parents were devout Catholics, and all of his siblings, like Leander, became saints. Leander first became a Benedictine monk; then, in 578, he was named Bishop of Seville. His brother Isidore succeeded him as bishop and was also canonized, as was his brother Fulgentius, who became bishop of Carthagena. His sister Florentina became a nun – in fact, she oversaw 40 convents and more than 1,000 nuns. St. Isidore wrote of his holy brother:

This man of suave eloquence and eminent talent shone as brightly by his virtues as by his doctrine. By his faith and zeal the Gothic people have been converted from Arianism to the Catholic faith.

Leander's parents, despite their strong faith, were strongly influenced by the teachings of the third-century heretic Arius regarding the nature of God – an old heresy which had persisted even to Leander's time.


What Was the Arian Heresy?

Hilaire Belloc called Arianism “the first of the great heresies.” It had its beginning with Arius, a third-century bishop in Alexandria, Egypt.

Arius promoted a different Christology from that accepted by the Catholic Church (and by all the major Christian denominations). According to the Arian heresy, the Father alone is God; the “Logos” or Son was a created being, formed out of nothing by the Father before the universe was created. There was a time, Arius believed, when the Son had not existed.


St. Leander Carries the Teachings of Nicaea into the 6th Century

As confusion arose in the Church because of Arius' teachings, the Emperor Constantine the Great convened the First Council of Nicaea in A.D. 325. The Council brought together bishops representing all of Christendom, for the purpose of studying the controversial teachings and ruling on their veracity. What, the bishops asked, was the relationship between God the Father and the Son (not only in his incarnate form as Jesus, but also in his nature before the creation of the world)? Are the Father and Son one in divine purpose only, or also one in being?

By an overwhelming vote, the Council Fathers ruled against Arius – insisting that the three Persons of the Blessed Trinity had existed eternally. Only two bishops disagreed; and they, along with Arius, were banished to Illyria. Among the major accomplishments of the First Council of Nicaea was the introduction of the Nicene Creed, which delineated the beliefs of the Catholic Church and thus offered a clear refutation of Arius' teaching. The Creed that emerged from this Council (and from the Council of Constantinople in A.D. 381) explained Jesus' identity in words we still use today:

I believe in one Lord Jesus Christ,
the Only Begotten Son of God,
born of the Father before all ages.
God from God, Light from Light,
true God from true God,
begotten, not made, consubstantial with the Father;
through him all things were made.

If this sounds familiar to you, you can thank Bishop Leander. He was the first to insert this Creed into the Mass, helping to ensure that ordinary Catholics through the centuries would better understand these key doctrines.

He also encouraged the papal legate, the future Pope Gregory the Great, to write the Moralia, his well-known commentary on the Book of Job. He presided over the third local Council of Toledo, which decreed the consubstantiality of the three Persons of the Trinity, and delivered the closing sermon at that council. As if all that weren't enough, he was also responsible for creating an influential Rule for nuns.

In his native Spain, St. Leander is recognized as a Doctor of the Church.