Language is a kind of code. It is a mnemonic for meaning. We use language to communicate meaning. Sometimes, we want to use it so as to include people and reach as many as possible, as for example in advertisements or in political speeches. Sometimes, we want to use it so as to keep a secret and exclude people.
Cryptography is the use of language in the second sense.
We can learn an unfamiliar language in many ways, but mostly by exposure to it. This is the idea behind immersion in a language, such as French immersion. It is the same principle in music or dance. What looks at first like meaningless sound or movement slowly becomes meaningful as we expose ourselves to it. The same applies to codes and that is why no code will live forever.