The second paragraph about ethical and doctrinal rules and standards raises a few questions:
Are there expressible ethical and theological (creedal) standards a Christian must abide by?
Sure. But in normal Protestant mode I see most of this as after one is a Christian. That is, given that one is a Christian there are things one has to do. They’re mostly not requirements to be accepted by God in the first place.
Are these standards universal
To some extent. God is one. Jesus is the Son of God. That’s not going to change between cultures or over time. Neither is love your neighbor. That Christ is one person with two natures is an attempt to explain the Incarnation in a terminology from a particular culture. In other cultures we can use other explanations.
That interest can’t be charged was an attempt to avoid taking advantage of the poor. With changes in economic system, loans with interest are now seen as allowing poor people to do things that they wouldn’t otherwise be able to do, though abuse is still an all too common danger.
Are these standards societal or individual; are these incumbent upon the Christian society, or on the Christian, or both
Both. There are certainly implications on both individual behavior and the right way to structure society and government.
Can these standards be expressed as rules and laws?
Are these rules and laws universal?
In some cases yes. We have laws such as prohibitions of murder. But then we have courts that work out traditional interpretations for exceptional situations such as self-defense. But if you look at Matthew 5, Jesus emphasized intent. There’s a limit to what you can accomplish with law and standards.
Not all are universal. Almost every society has laws against murder, though I don’t know enough legal history to know how the details may differ across cultures and over time. But we’ve recently tried to codify abuse against children. This was always wrong and there were always some laws, but standards have been getting stricter and laws more explicit. Slavery was once considered acceptable, but no longer is. There have been major changes in principles involving family and sexual activity. Some of these are because of changes in how Christians understand Christian teaching, others because of differences in economic and cultural institutions. Most of these changes are controversial among Christians.
This is why Jesus gave the power of the keys to the Church(es). It’s to allow us to interpret the implications of the Gospel in specific situations and with specific challenges.
But I would maintain that it’s a judgement call where we use
* general standards such as love and forgiveness
* more specific guidelines such as not looking at someone with lust
* specific rules, such as when killing is and isn’t permitted
* law (by which I mean governmental enforcement)
Making too many specific rules or laws is one kind of legalism.
It’s also worth noting that Paul recognized that there will be situations where Christians simply disagree. One of the issues he faced was eating meat that has been sacrificed to idols. He had has own position, but was primarily concerned that Christians who took different views should still respect each other as faithful Christians.
I make a distinction above between standards and laws. The former refers to their existence and necessity, while the latter refers to their application and articulation.
I think there may be more than two categories. I tried to outline them above.