The Formula of Union, approved by Pope St. Sixtus III: “But how we know and speak regarding the Virgin Mother of God, and about the manner of the incarnation of the only-begotten Son of God, necessary not because of increase but for satisfaction, we have taken and possess from above, from the divine Scriptures as well as from the tradition of the holy fathers, and we speak briefly, adding nothing at all to the faith of the holy Fathers, which was set forth at Nicea. For, as we have already said, this suffices for all understanding of piety and for all renunciation of heretical perfidy. But we speak not presuming the unlawful, but by confession of special weakness excluding those who wish to rise up against what we regard as beyond man.”