Heresy bends the confession of Christian truth to the norms of the culture and away from the Word of God. As such it is a spirit of accommodation.
Christian doctrine is then no longer what is believed, taught, and confessed on the basis of the Word of God. Christian doctrine when it is infiltrated by heresy conforms to human thought, very often the spirit of the age, and always to the desires, expectations and limits of fallen reason and affection. It is wise then for teachers in the church to be familiar with the form and content of unbelief in their day. These ideas may well surface in the church as new light on the Bible and the way forward theologically. But teachers in the church must also be aware of the deep currents of unbelief that swirl around in the fallen imagination and hearts of men and women.
Both of these sources of heresy could be found in Socinianism:
"Faustus Socinus (1539-1604) was something of a Renaissance prophet whose rationalism eventually led him to deny almost every cardinal Christian doctrine, including the deity of Christ, predestination, original sin, total depravity, vicarious atonement and justification by faith.
Socinianism, which had its roots in older heresies such as Arianism and Pelagianism, struck a responsive chord in a generation influenced by Renaissance humanism's optimistic view of humanity. Like the Remonstrants, Socinians tried to interpret Christianity to accommodate the views of the Renaissance.
In the eighteenth century, Socinianism influenced English Baptists and Presbyterians and, in New England, Congregationalists, eventually culminating in Unitarianism on both sides of the Atlantic. In the nineteenth century, Socinianism gained adherents among Quakers in the United States. In form and content Socinianism can hardly be distinguished from the modernism of the late nineteenth and twentieth centuries."
Joel Beeke, "The Atonement in Herman Bavinck's Theology," in Hill & James (eds), The Glory of the Atonement, p. 340-1