Pope Saint Agatho (reigned 678-681) is interesting for two reasons. The first is that Pope Agatho was ethnically Greek. He would make a fine patron saint for Greek Catholics who honor both the papacy and the Greek patrimony.*

The second interesting fact about Pope St Agatho is that was the author the Papal Oath that popes have recited when assuming the duties of Saint Peter as the Vicar of Christ on earth.

Why did Saint Agatho write a papal oath? Pope Saint Agatho’s predecessor, Pope Honorius (reigned 625-638) had tolerated the monothelite heresy (the false belief that Christ has only one will – a divine will). This papal toleration of heresy had led to confusion within the Catholic Church, and Pope St Agatho wanted to ensure that all future Popes would manfully defend the one true Faith, without which it is impossible to please God.

Here is the text of the Papal Oath authored by Pope Saint Agatho:

I vow to change nothing of the received Tradition, and nothing thereof I have found before me guarded by my God-pleasing predecessors, to encroach upon, to alter, or to permit any innovation therein;

To the contrary: with glowing affection as her truly faithful student and successor, to safeguard reverently the passed-on good, with my whole strength and utmost effort;

To cleanse all that is in contradiction to the canonical order, should such appear;

To guard the Holy Canons and Decrees of our Popes as if they were the Divine ordinances of Heaven, because I am conscious of Thee, whose place I take through the Grace of God, whose Vicarship I possess with Thy support, being subject to the severest accounting before Thy Divine Tribunal over all that I shall confess;

I swear to God Almighty and the Savior Jesus Christ that I will keep whatever has been revealed through Christ and His Successors and whatever the first councils and my predecessors have defined and declared.

I will keep without sacrifice to itself the discipline and the rite of the Church. I will put outside the Church whoever dares to go against this oath, may it be somebody else or I.

If I should undertake to act in anything of contrary sense, or should permit that it will be executed, Thou willst not be merciful to me on the dreadful Day of Divine Justice.

Accordingly, without exclusion, We subject to severest excommunication anyone — be it ourselves or be it another — who would dare to undertake anything new in contradiction to this constituted evangelic Tradition and the purity of the Orthodox Faith and the Christian Religion, or would seek to change anything by his opposing efforts, or would agree with those who undertake such a blasphemous venture.

Source: Liber Diurnus Romanorum Pontificum (Migne’s Patrologia Latina 1005, S. 54)

   * There have been a number of Greek Popes:

Pope Agatho
Pope Anterus
Pope Dionysius
Pope Eleutherus
Pope Innocent VIII
Pope John VI
Pope John VII
Pope Sixtus II
Pope Telesphorus
Pope Theodore I
Pope Zachary
Pope Zosimus

It’s interesting to think that if a Greek Catholic should be elected to the Chair of Saint Peter as Pope, he would de facto conform to the Latin Rite – though he would also be free to celebrate the Eastern liturgies since Holy Father is “pan-ritual” by virtue of his universal jurisdiction over all rites.