[5][6] During his pontificate he called for strict Catholic orthodoxy, more assertively demanded obedience to papal authority, and, consequently, increased the tension between the Western and Eastern Churches.

The split with the Emperor and the Patriarch of Constantinople was inevitable, from the Western view, because they adopted the Monophysite heresy of Jesus Christ having only a Divine nature.

[12] Closer to home, after a long contest Gelasius finally suppressed the ancient Roman festival of the Lupercalia,[10] which had persisted for several generations among a nominally Christian population.

Gelasius' letter to the Senator Andromachus treated the primary contentions of the controversy and incidentally provided some details of the festival, which combined fertility and purification, that might have been lost otherwise.

The attribution to Gelasius is premised in part at least on the chronicle of the Supreme Pontiffs that is denominated the Liber Pontificalis, which states of Gelasius that he "fecit etiam et sacramentorum praefationes et orationes cauto sermone et epistulas fidei delimato sermone multas" ("he also made prefaces to the sacraments and prayers in careful language and many epistles in polished language regarding the faith").

The section read: "Grant, We beseech Thee, O Lord, that we do not trouble ourselves about the contradiction of spurious minds, but once that very wickedness has been spurned let us pray that you suffer us neither to be frightened by the unjust criticisms, nor to be attracted to the insidious flatteries, but rather to love that which Thou dost command ...".

[16] The primary source for the biography of Pope Saint Gelasius I, beside the Liber Pontificalis, is a vita written by Cassiodorus' pupil Dionysius Exiguus.