Other churches discuss this verse as having something to do with correcting "our brother's sins." I am not a fan of that concept! I have understood this verse differently; as a student of Unity teachings, I am very interested in a Unity translation. What does it mean, "where two or more are gathered in my name, I am there in the midst of them?"
The whole of Chapter 18 in the Gospel of Matthew consists of Jesus's instructions to his disciples on how to continue his ministry after he has left. He is speaking as the Christ—the eternal spiritual Truth that Jesus has made manifest through his human experience. His purpose has always been to each of us to discover that the Christ is also the spiritual Truth of each of us, and the possibility exists for us to make the Christ manifest just as he did. The key instruction of verse 20 is basically that it's much more difficult to achieve this Christ awareness if we try to do it alone. When we come together—as we in Unity do each Sunday—we find it easier to see the Christ expressing as each other than it is to see it in ourselves. And seeing it in each other becomes an easier path to recognizing it in ourselves.