How do we know which Scriptures are applicable to our lives today (those regarding homosexuality and divorce, for example) and which are discounted as "culturally irrelevant" (like greeting with a holy kiss or women covering their heads, etc.)?

I think there are principles that can help us answer almost all the questions, and then there are going to be some gray areas.

I think the holy kiss is a gray area. Why did he say that ("Greet one another with a holy kiss")? Does that mean "shake hands"? Or does it mean "do some culturally-appropriate significant act of affection"? Why wouldn't that be a kiss?

I know men who, when I meet them, kiss me. I won't name them, but they're friends. It has zero homosexual implications, and they are very manly, and it is deeply moving. They kiss me on the cheek. I see them a year later, they hug me, and then they kiss me on the cheek.

That's why I say that the holy kiss to me is not a done deal. Maybe we should. But maybe we shouldn't. Maybe an embrace is good enough, and in our culture a kiss might not be as appropriate as it was then.

The question here though is: How do you decide?

My answer is

1. To the degree that a stipulation is rooted in creation, to that degree it has abiding value. Marriage would be huge in that regard.
2. To the degree that it is commanded across the whole terrain of Scripture—Old, New, Epistles, Gospels—it has high level abiding validity.
3. And to the degree that it is related to the gospel and close to the gospel it has ongoing validity and staying authority.

And so I think those three qualifications generally will answer almost all of our questions.

A fourth one would be: If the New Testament invalidates anything in the Old Testament that was commanded (like sacrifices or the priesthood or circumcision—things like that), that's another criterion so that these are not required anymore.

But on the ones that are culturally governed, I think the criteria of whether they are 1) rooted in creation, 2) commanded across the whole terrain of Scripture, and 3) closely connected and growing out integrally, organically from the gospel will go a long way to answering almost all of our questions.