This poem, which develops the legend of a student in Oxford who left his studies to become a vagrant, captures the elegaic happiness of a life lived away from the pressures of society, which Arnold thought to be so destructive and negative. The scholar-gypsy, by contrast, is free to wander and live outside the "repeated shocks" that "exhaust the energy of strongest souls" in society. The mood that is therefore created is one in which Arnold summons up a world that he believes is lost to the "modern life," a pastoral landscape of beauty, happiness and peace. Note how this mood of tranquility is created in the following quote:
On some mild pastoral slope
Emerge, and resting on the moonlit pales
Freshen thy flowers as in former years
With dew, or listen with enchanted ears,
From the dark dingles, to the nightingales!
Nature is depicted as a force for human renewal, whose beauty and solitude is balm to the human soul. Note how this quote engages different senses with not only the sight of flowers, but also the feel of the "mild pastoral slope" and the sound of "nightingales." All these aspects are part of the presentation of nature as a force for good and for healing, which helps create the overall tranquil mood of elegaic happiness.
You can determine mood by asking yourself this question: How does the poem make me feel? Then, go back through the poem and find words that match the feeling you have. If the feeling and the words match- you have determined mood.
mood = emotion the author indends the audience to feel