I think understanding resonance is really important, and I thought my explanation came out well in my recent newsletter. I've copied part of it and put a link to the browser version of it at the bottom of this mini-blog post. If you want to get newsletter each month, it's free to sign up for and easy to unsubscribe from.
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From the April 2012 Edition of The Wake Up Call:
"You may have heard people say things like, "That really resonates with
me." You may have used this phrase yourself, or you may have no idea
what this term means. Simply, it means something feels true. However,
resonance may not always feel good. Sometimes, the truth strikes us very
strongly, and the resounding chord inside of us feels very
uncomfortable. Someone can say something so true that you can feel
strongly upset--scared, angry, or what-not. In these moments, I refer to
this type of resonance as been activated (I use activate and activation
very differently than the usual New Age jargon, by the way). This type
of resonance is just as important as the one that feels really good, and
I'll offer some tips below about how to get better at interpreting
resonance and being with it."
Read more from my April newsletter about resonance.