It was from San Gregorio that Pope Gregory the Great sent the monk Augustine with 40 companions to evangelize Britain in 597. Because of its historic roots, Anglicans widely consider the church to be their "motherhouse."
In their joint-declaration, Welby and Pope Francis recognized that both Catholics and Anglicans "are heirs of the treasure of the Gospel of Jesus Christ and the call to share that treasure with the whole world."
They noted that since that first public meeting in 1966, "much progress" has been made in terms of overcoming the obstacles that stand in the way of unity.
However, the modern times have led to new hiccups in the process, particularly surrounding the topics of the ordination of women and "more recent questions regarding human sexuality."
"Behind these differences lies a perennial question about how authority is exercised in the Christian community," the declaration read, recognizing that these concerns constitute "serious obstacles to our full unity."
Yet while solutions to these questions remain in question, Francis and Welby said they are "undeterred" in their quest for unity.
These differences "cannot prevent us from recognizing one another as brothers and sisters in Christ by reason of our common baptism," nor should they "hold us back" from discovering the faith and holiness of each other's traditions, they said.
Neither should differences get in the way of common prayer, the prelates cautioned, and urged their respective clergy and faithful "not to neglect or undervalue that certain yet imperfect communion that we already share."
A shared faith and joy in the Gospel are stronger than the differences, they said, stressing that "the world must see us witnessing to this common faith in Jesus by acting together."
Common points of collaboration mentioned include working together to protect creation and promote "a sustainable and integral development for the good of all, and to uphold the dignity of the human being in all states and stages of life.
Centuries of painful separation have been "partially healed by 50 years of friendship," they said, adding that "we have become partners and companions on our pilgrim journey."
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As fellow Christians, the Churches are facing the same difficulties, while also strengthening each other "by learning to value the gifts which God has given to the other, and to receive them as our own in humility and gratitude."
The two prelates made reference to the 19 pairs of Catholic and Anglican bishops commissioned during the Vespers ceremony, praying that their ecumenical mission would be "a witness to all of us."
"Let the message go out from this holy place, as the Good News was sent out so many centuries ago, that Catholics and Anglicans will work together to give voice to our common faith in the Lord Jesus Christ, to bring relief to the suffering, to bring peace where there is conflict, to bring dignity where it is denied and trampled upon."
The two exchanged gifts at the close of the ceremony. Pope Francis gifted Archbishop Welby a replica of the hook-like head of the crozier of St. Gregory, while the archbishop in a strong show of unity took his pectoral cross made out of nails from the roof of the Anglican Coventry Cathedral and gave it as a gift to Pope Francis, who kissed it.
Both Pope Francis and Archbishop Welby gave homilies during Vespers, which was prayed in Latin. The prelates both emphasized that while their traditions might be different, a shared baptism and commitment to spreading the Gospel unites them.
Pope Francis in his homily prayed that the encounter would give rise to "a renewed impetus toward communion and mission," while Welby, for his part, noted that while it might be tempting to look back, the prophets "compel us to look forward...we cannot be bad shepherds."