The opening and ending themes of "Summer Time Rendering" play a crucial role in setting the tone and atmosphere for each episode. The opening theme is designed to introduce viewers to the overall mood and themes of the series, giving them a glimpse of what to expect. On the other hand, the ending theme serves to reflect on the events of the episode and leave a lasting impression on the audience. The music and visuals in these themes can also provide subtle hints and foreshadowing of future developments in the story, adding another layer of depth to the viewing experience.