You should have Googled Gestalt Reality because that explains what's going on. The phrase "The sum of the parts is greater than the whole" explains it, but in Gestalt Reality the sum of the parts is a whole new being. Like your 'parts' A part/aspect of you is your Soul, another is your brain, mind, consciousness, subconscious..... All those parts create you as a whole being, and if one of them was taken out of the equation you'd fall apart. Add a touch of Fractal Geometry for visualisation and "We are One," because you and every other individual is a part of the bigger fractal pattern. You are a fractal, the people that are on this thread can be thought of as another layer of the fractal and so on until you get to God him/her/itself.

Or you could do some Sacred Geometry with the Vesica Pisces, Buddhist Egg of Life and Tree of Life. It's all bigger picture stuff and different perspectives or ways to understand the same thinking.

If you prefer something simpler then they have a saying in Africa - "Ubuntu," which means "I am because we are." Inter-relationships and inter-connectedness of individuated aspects of God/Universe/Source. Here's the doozy though. This "We are One" assumes that the perspective is that we are individuals trying to work out how We Are One. Another belief is that we are individuated aspects of the One/God/Source, so we are not individuals thinking We Are One, we are One thinking we are individuals. In that context you have it backwards.