What is Heresy?

[Hazelelponi]

I'm asking this in earnest, not as a critique but out of genuine curiosity. I’ve spent a lot of time over the last few years trying to sort out what actually constitutes Christian belief, and in that process I’ve written off quite a bit as “not Christian.” So I want to be thoughtful in how I evaluate things going forward now that I am sure of home.

As many probably already know (and has been pointed out) Dispensational premillennialism is not typically treated as a heresy, even if it's in opposition to a classical doctrine. That got me wondering:

Are there other issues—especially ones that might appear more peripheral to some—that would actually be considered heterodox or even heretical by historic, conservative Christian standards?

For instance:

• The ordination of women as pastors, elders, or deacons
• The acceptance of homosexual marriages

Would either of those positions be seen as heretical? Or are they generally considered secondary issues that fall within the bounds of orthodoxy as long as someone affirms core creeds like the Trinity, the resurrection, and salvation through Christ?

I guess what I’m really asking is: How do we rightly discern what marks the boundaries of the church’s teaching? How do we evaluate the visible church when serious disagreements exist over things that touch on moral and ecclesial order?

Again, I'm not trying to stir controversy—I truly want to understand how to think through these matters.