From a Japanese PoV, what's the explanation of 「に」 particle corresponding to both western concepts of "to" and "in"


> 自由に歩いて。
>
> 人の中に心臓がある。
>
> 学校に行きます。

If I'm correct:

  1. Walk freely. (Walk in freedom)

  2. Inside a person there's a heart.

  3. I go to school.

So, I'd want to understand why 「に」 covers both "to" and "in".

A possible theory that I have thought of is that in sentences similar to 2,
the literal translation is in fact: "There's a heart to (に) the inside of a
person" Is this solution correct? Am I missing something or some cases for
which it wouldn't be correct?

Also, as in sentences one, why are na-adj. followed by 「に」 rather 「で」when they
explain a manner?

