Too Hard
There are at least three working definitions of heresy. First is the view that all error is heresy. This view has as an advantage that it recognizes the unity of truth. Because God is one, and God is truth, truth is one. Any error that we hold, if carried to its logical conclusion will lead us to wicked, damnable errors. If we adjust all that we think to make it consistent with the error we hold, we will enter into heresy. The disadvantage to this view, like many broad definitions, is that it draws the circle too wide. If we are all guilty of error, and if all error is heresy we are certainly all guilty. Which makes no one guilty. Definitions exist to differentiate, not to be all-inclusive.
Too Soft
A second view holds that heresy is holding to any doctrine specifically condemned as heresy at an ecumenical council. The Arian heresy, which denies the deity of Christ, was condemned as heresy in the first half of the first millennia of the church. The Pelagian heresy was likewise condemned. This view has as an advantage being tied to the labors of the church at its broadest. That is, it is the church as the church that names the heresy, rather than each of us as individuals. It has as a disadvantage the hard truth that there have been no ecumenical councils in quite some time. Such would be rather hard to pull off in our day. Heresy, however, is rather easy to pull off. This view ends up with too narrow of view of what heresy is.
Just Right
My own view is in the middle of these too positions. I agree with the second view that all those views which have been condemned as heresy by ecumenical councils are in fact heresy. I would add, however, that any denial of any element of any ecumenical creed, including the Apostles’ Creed, is heresy. That is, to avoid the charge of heresy, one must not only not embrace what the councils call heresy, but must affirm what the councils call orthodoxy. In light of the inability to put together an ecumenical council, indeed in light of the inability to reach agreement among all those claiming to be Christian churches, I would also add, though it is in the Apostles’ Creed only by implication, that one must affirm justification by faith alone in order to not be heretical. This doctrine Luther wisely called the article on which the church stands or falls.
Most of those councils which included condemnations of heresy dealt with issues of the incarnation and the Trinity. These are, of course, critical issues to the church. They should not, however, be given a privileged position about all the other affirmations of the Apostles’ Creed. To deny the resurrection, for instance, is as much heresy as to deny the humanity of Christ. To deny the virgin birth is as much heresy as to deny the two natures of Christ. Which means of course, that we have no unity with those who deny any of these things, whether we find these heresies in mainline denominations, or as in the case of denying the resurrection, whether these are held by those who would otherwise describe themselves even as “Reformed.” That is, among some of the hyper-preterists.
If my perspective is accurate on justification by faith alone, that too sets us apart from both Rome and Eastern Orthodoxy. Rome, which while in substantial agreement with Eastern Orthodoxy, but which speaks to the matter with greater clarity, not only does not affirm that we are justified by faith alone, but formally and unchangeably affirms that all of us who affirm that a man is justified by faith alone, apart from the works of the law, should be damned. See the sixth session of the Council of Trent.
To name heresy what it is is not to be unkind or unloving. It isn’t bigoted or narrow- minded. It is instead to guard the wisdom that has been handed down to us, and to protect His sheep from wolves. Truth be told, everyone, no matter how broadminded, draws lines somewhere. The only question is, are we drawing lines where God would have us draw lines? The answer to that, in the end, is found in His Word.