Okay, so a lot of the New Testament Greek is conversational prose. Why isn't this evident in the KJV? Parts of Galatians in the KJV is hard to read.
Their intent was to create a beautiful and accurate (as best they could) translation in the language of the day that was better than the "vulgar" versions, although:
§13 An answer to the imputations of our adversaries
• 1 Now to the latter we answer, that we do not deny, nay, we affirm and avow, that the very meanest translation of the Bible in English, set forth by men of our profession, (for we have seen none of theirs of the whole Bible as yet) containeth the Word of God, nay, is the Word of God. (from the Translators to the Reader notes)
The preceding comment completely undermines the idea that only the King James Bible is valid in the English language. The very translators of the King James rejected that their translation was the only valid one.
It was written to appeal to the King and educated men, as well as the common man. However, the English language is always changing, with the meaning of words changing or going obsolete and new words coming into use. That 400 year distance from the original KJV has made it difficult for many of us to read.
You said that that in order to communicate with others, you polish your words to remove everything that detracts from its clarity.
Yes, I always try to do that in my written communication.
But do you also remove authorial voice? In other words, suppose you want your prose to sound a certain way, do you abandon this just for the sake of clarity?
I'm not certain as to exactly what you mean by "authorial voice," but sometimes I will introduce a piece of writing (let's say, for a magazine article on history), with a vivid and poetic short introductory paragraph (maybe three sentences) to set the scene. Then I simply tell the story. At no time do I make reference to myself.
In other writing, such as a personal essay or meditation (for instance, a devotional), I might tell of a very brief story from my childhood to illustrate a point or set up the idea being explored. But I try to 'make room' for the reader to find themselves in the story by keeping myself out of it as much as possible. The goal is to walk through the thoughts together, not simply report back what I have learned.
Or is it actually impossible to make it sound that way while being as clear as possible?
It's very hard to do both, but some gifted writers can do it. The big danger is that the writing can often turn into an exercise of one's ego. The reader can sense when the author is telling the story for the benefit of the reader, or if the author is simply a narcissist. A successful author builds a relationship with the reader by serving them with humility and not trying to impress. Plainly written prose can be extremely powerful, something greater than the sum of its parts.
I'll leave you with this famous example of well-written, simple prose that was given as an extremely short speech. The author uses a memorable and interest grabbing first sentence and then speaks directly to their common lived experience in the next four sentences. And then he gets to the profound meat of his message:
Four score and seven years ago our fathers brought forth on this continent, a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal.
Now we are engaged in a great civil war, testing whether that nation, or any nation so conceived and so dedicated, can long endure. We are met on a great battle-field of that war. We have come to dedicate a portion of that field, as a final resting place for those who here gave their lives that that nation might live. It is altogether fitting and proper that we should do this.
But, in a larger sense, we can not dedicate -- we can not consecrate -- we can not hallow -- this ground. The brave men, living and dead, who struggled here, have consecrated it, far above our poor power to add or detract. The world will little note, nor long remember what we say here, but it can never forget what they did here. It is for us the living, rather, to be dedicated here to the unfinished work which they who fought here have thus far so nobly advanced. It is rather for us to be here dedicated to the great task remaining before us -- that from these honored dead we take increased devotion to that cause for which they gave the last full measure of devotion -- that we here highly resolve that these dead shall not have died in vain -- that this nation, under God, shall have a new birth of freedom -- and that government of the people, by the people, for the people, shall not perish from the earth.
Abraham Lincoln
November 19, 1863