While heresy takes various forms, I’m inclined to view all heresy as having an underlying unity: opposition to the Incarnation. As is written in 1 John 4:2
By this you know the Spirit of God: every spirit which confesses that Jesus Christ has come in the flesh is of God
Denying that confession takes various forms and even the mistaking of ‘reconciliation’ to be with the dominant political opinion rather than with God has, I think, a connection with mistaking the Incarnation. As we endeavor to respond graciously and irenically to this mistake, it is useful to read what the early saint, Irenaeus, had to say against the heresies. Hans Urs Von Balthasar has edited a useful selection of St Irenaeus’ writings titled ‘The Scandal of the Incarnation’, about which the publisher of the English translation writes:
Saint Irenaeus was the first great Christian theologian. Born in Asia Minor in about 130 A.D., he became Bishop of Lyons and died as a martyr early in the third century. His main work, Adversus Haereses (Against the Heresies), is as relevant today as it was eighteen hundred years ago. It is a critique of Gnosticism, the ‘anti-body’ heresy, which, far from dying out, continues to flourish as the main threat to the Christian faith in our own day. With serenity and good humor, Irenaeus unfolds the unity of God’s purpose in creation and redemption, in Old and New Testaments. The flesh and blood which Gnosticism so despised has been assumed by God in the womb of the Virgin Mary, and glorified in the Resurrection and the Eucharist.
In this book, quotations from Saint Irenaeus have been arranged thematically in order to show the unity of his Christian view of the world. The texts have been selected and are introduced by the late Hans Urs von Balthasar, who is widely regarded as one of the greatest Catholic theologians of this century. They are translated by John Saward. “Everything in Irenaeus is bathed in a warm and radiant joy, a wise and majestic gentleness. His words of struggle are hard as iron and crystal clear, … so penetrating that they cannot fail to enlighten the unbiased observer.”
— Hans Urs von Balthasar