Taken from Rorate Caeli
From the origin of Christianity, all heresies have had the same character, and, long before the age of Arius, Tertullian had said, "Heretics vary in their rules; namely, in their confessions of faith. Every one of them thinks he has a right to change and model what he has received according to his own fancy, as the author of the sect composed it according to his own fancy. Heresy never changes its proper nature in never ceasing to innovate...". ...
This nature of heresy has always been observed by Catholics and two holy authors of the eighth century wrote that "heresy, however old, is always in itself a novelty; to better retain their title of novelty, [heresy] innovates daily and daily changes its doctrine."
But, while heresies always vary, never agreeing among themselves and continuously introducing new rules..., Tertullian says that "in the Church, the rule of Faith is unalterable, and never to be reformed". It is so because the Church, which professes to speak and teach nothing but what she has received, does not vary; heresy, on the contrary, which began by innovating, innovates daily, and does not change its nature. ...
Two aspects cause this disorder of heresies: one drawn from the nature of the human mind, which, having once tasted the temptation of novelty, does not cease to seek with disordered appetite this deceitful allurement; the other originating from the difference which exists between the works of God and those of man.
The Catholic Truth proceeds from God and has its perfection at once; heresy, the frail offspring of the human mind, can be formed only by disordered patches. When ... we venture to remove "the ancient landmarks established by our Fathers" and to reform the doctrine once received among the faithful, we set events in motion without the slightest insight into the consequences of our attempt.
Jacques Bénigne Bossuet
Histoire des variations des églises protestantes