The ego is a veil between humans and GOD.
Rumi's definition of the ego is brilliant. The word ego is just a fancy Latin word for the "I", so his message is that more often than not our "I" experience prevents us from enjoying the GOD CONNECTION. "I" as in interference, I would say. Or, keep the "I" at bay and you can enjoy the WAY.
We spiritual travelers have experienced many spiritual break-throughs. The blessed moments when the mind stands still and the occasions when the holy NOW completely captures us. It is in these magic occasions when the "I" experiences what the observer knows is the WAY.
The "I" need not interfere with the WAY. When we are open to the holy NOW, the "I" becomes part of something much bigger and more magnificent. The "I" simply melts in the presence of the GOD CONNECTION. The "I" becomes part of the "I AM THAT I AM" experience.
Don't try to beat the "I" into submission, it can't be done anyway. Enjoy life instead every step of the WAY. Truth be told, we can't control the "I" but we can open up to GOD's many messengers. The beauty and the magnificence of the WAY keeps the "I" at bay.