The mood in a piece of literature depicts the feelings or emotions of the piece. When analyzing for mood, things that are helpful to look for are imagery and language. Imagery refers to the words that create a mental picture for the reader, especially words that relate to the senses. Such images can produce an emotional effect, which helps a reader to understand the author's tone. Individual word choices, referred to as diction, can also produce an emotional impact. Authors are very careful about word choices because each word has different connotations that convey different meanings. Even sound alone can produce an emotional effect. In addition, the mood of a literary piece can help convey its meaning because emotions help express meaning. Due to space limitations, we can't analyze all of the chorus's odes for mood in Oedipus Rex, but below are some ideas to get you started.
The mood in the first choral ode especially expresses the chorus's fear and reverence for the gods, showing us that the meaning of the ode is simply to describe the city's desperation and desire for salvation from the gods. They see the gods as both their preservers and their destroyers. In this ode, the chorus is waiting in anticipation for the prophecy from Apollo that they hope will tell them what needs to be done to end their present plague and please the gods once more. Since they see the prophecy as a chance to become saved by the gods, we see the chorus express their admiration for the gods, especially in the words found in the opening phrase, "O sweetly worded voice of Zeus" (163). The chorus also expresses its fear of the gods, as we see in the word choices in the line, "My frightened mind shakes in fear, quivering" (165). We especially see the chorus's view that the gods have both the ability to save and destroy in the phrase "o healing Delian Paean" (166). In this phrase, "Delian Paean" refers to Apollo as a healer (eNotes, Oedipus Rex). All of the diction used to paint the gods as both the city's preservers and destroyers, serves to paint the chorus's mood of feeling both in awe of the gods and fearful of the gods. Their mood is especially one of desperation because of the city's suffering due to the current plague.
We can especially hear the chorus's mood of desperation and agony in the chorus's use of images to portray the growing numbers of dead citizens, as we see in the lines:
Unable to count their number,
the city is destroyed, and unpitied,
their generations lie upon the ground. (188-190)
The image of uncountable numbers shows us that a great many of Thebes' citizens have died. The image of generations lying on the ground also helps us to see just how many people, both young and old, have died, showing us the desperate mood of the chorus and conveying the chorus's meaning, which is to petition the gods for help.