An Chead Drama is basically a poem where the poet reflects on a person's life. He describes the world as a stage full of actors appointed by God (us). He uses the idea of a prompter behind a curtain to describe the way in which we are tempted daily by the devil. He sees God as the presenter and adjudicator who will decide who gets the prize (heaven) and who doesn't (hell) when they die.
He reflects on his own life and acknowledges that he made mistakes. Or, in keeping with the stage analogy, didnt know his lines. He does however pledge his allegience to God at the end of the poem and dismisses the devil, even though he didn't always manage to do this during his life.
Hope this helps. I know it's very brief and basic but it gets across the main points.