People in glass houses shouldn’t throw rocks.

What would happen if someone in a glass house threw a rock? Well, it would probably break the house. The idea with this phrase is that you shouldn't criticize others for flaws that you have as well. It is a saying about hypocrisy.
It is a strange phrase to understand. But think about it like this. If you are in the glass house, people can see your faults. You can see the same faults in people walking by (but they can also see you). If you throw the stone, you are only going to destroy your own house.
I think it is easier to understand through Benjamin Franklin's retelling: "Don't throw stones at your neighbors', if your own windows are glass."

For more English phrases and quotes, follow me on Facebook:
https://www.facebook.com/ESL-ToyBox-112152010890485