The Nature of Enlightenment
Q: What does it mean to be enlightened – does it mean being free of suffering? Once a person reaches the first phase, can you “lose” enlightenment?
A: People define enlightenment differently. I like the expression: sudden awakening, gradual cultivation, sudden awakening, gradual cultivation, sudden awakening . . . . in lovely circle, or spiral, with no point of beginning. Or the traditional phrase: moments of enlightenment . . . many times a day.
In early Buddhism, enlightenment is conceived of in four stages, starting with stream entry and ending as an arahant. I like the way enlightenment is operationalized for an arahant: irrevocably (which gets to your query about losing enlightenment), greed, hatred, and delusion (broadly defined) no longer arise in the mind at all, or perhaps arise subtly and occasionally but can find no hold. That’s a psychologically meaningful definition I can relate to.
In effect, we are already enlightened (in the sense of always already having Buddhanature; it’s just obscured by the usual crud) . . . and we have moments of awakening that inspire and purify us . . . we need to practice . . . over time, those jewel-like moments become deeper, longer, and more stable . . . gradually stitching together at the highest levels into a seamless necklace of unconditional love and inner peace. Pretty good news!