When internet posts are mis-interpreted so easily, how can we be sure of a correct interpretation of bible passages now that the writer of said passages cannot be questioned in person?
Not
every internet post is misinterpreted. A great many aren't. In my experience, the problem isn't that my posts aren't clear, but that people come to my posts with certain personal filters, and prejudices, and presuppositions and read what I've written through them, sometimes badly contorting what I've written as a consequence. The problem, then, isn't with the clarity of what I wrote but with the confusing lenses through which people will read what I wrote.
A good interpretive hermeneutic can go a long way to countering the contorting effects of our personal "lenses":
1. Immediate context is king. It defines and constrains what meaning we give to any verse or passage.
2. Can my interpretation of a verse or passage be solidly reconciled to the rest of Scripture?
3. To whom was the verse or passage written?
4. What sort of literature is the verse or passage I'm reading? Poetry? Prophecy? Wisdom literature? Historical account? What bearing does the genre of a particular verse or passage have on how I understand its meaning?
5. Avoid eisegesis.
6. What was the cultural context in which a verse or passage was written? Does a knowledge of this context aid in understanding the verse or passage?
7. Consider root meaning and common (historical) usage of words and phrases.
8. Avoid reading modern ideas and meanings into ancient verses and passages.
9. Avoid prooftexting. That is, removing a single verse, phrase or word from its immediate context and stringing it together with other verses, phrases or words torn from their contexts to form a doctrine. (This is really just a restating of point #1.)
It is...interesting that your OP question assumes the very thing it questions. You wrote your question assuming that it would be understood as given, though the question itself asserts that it may very likely be misinterpreted. As I read the responses of folks so far in this thread, I don't see that your OP has been badly misinterpreted, which rather defies your concern expressed in it.
The Bible is not, of course, an internet post. There are four Gospels, supporting and qualifying each other, and together providing a very fully-orbed description of the life and teaching of Christ. One can cross-check and compare among the Gospels, arriving at a very full idea of what Christ did and what he taught.
Thematically, the Bible is an astonishingly coherent text, enabling a reader to trace many themes from Genesis right through to John's Revelation. The many books of the Bible also act upon each other much as the Gospels do to each other, qualifying, clarifying and constraining the meaning of any one word, verse, or passage.
Then, too, the Christian has the Holy Spirit as Teacher, applying the truth of God's word to the believer's life, making it a part of the fiber of the believer's being, transforming and conforming them according to Scripture.
I don't see, then, that your worry that the Bible cannot be rightly understood as particularly valid. I suspect much of the modern concerns along this line stem from postmodernist philosophy that seems to have insinuated itself into nearly every region of human thought and endeavour. "There is no absolute truth!" postmodernism asserts; "Question and doubt everything!" it urges; "There is no true, objective right and wrong, only your truth and my truth," it proposes. But if one takes these ideas to heart, trying to comprehend the absolute, objective, exclusivistic, divine truth of Scripture has to be impossible, for no such truth, on postmodernism, exists.