The Birth of Jesus
One of the loveliest little plays I've ever read is an anonymous medieval work known as The Birth of Jesus, a play in series commonly called the Corpus Christi Cycle. The text I've linked is in Middle English, but it's not too bad. I first read it in grad school, and I reread it every year. My favorite lines are Joseph's words after he returns from a cold night of gathering firewood. Jesus was born while he was away, and he comes into the stable with an earnest but ordinary greeting, "Say, Marye doghtir, what chere with thee?" She answers that she's as good as she's ever been, and after what I can imagine was staged as a double-take, Joseph exclaims, "O Marye, what swete thyng is that on thy kne[e]?"