A rare and beautiful thing shared among humans. A thing you are not just the recipient or giver of, but something you are both to one another.
No one knows how it happens, since it isn't the result of some tumultuous exchange of deep dark secrets nor the end product of shared silly antics or endless repetition. You just open yourself and they do the same and for the rest of your time together, you allow each other to been truly seen and understood.
In a book called Friends for the Journey, there is a description of a pastor who was visiting a congregation in another country, where he didn't speak the language. He asked his translator how to say 'thank you' to the church's member, to which he was told that there was no direct translation for that phrase. "Thanking someone isn't something you say," replied the translator. "It's something you do."
Like love, having a kindred spirit isn't something you can easily describe. You just know it when you have one. You finish each other's thoughts, both spoken and unsaid. You easily forgive spoken or written errors because you know what they meant, and you can follow even their most frayed lines of thought. No one can get into the sphere you share. It is closer than lovers, closer than family, because neither of the two are required. It is something entirely outside the globe of reason, outside the despondant illusion that no one understands us that we are subject to every day.
I highly recommend them.