In this poem, Wordsworth compares his loneliness to a cloud drifting upon the breeze.  But then, he comes across a field of beautiful daffodils, and they are so beautiful that he spends a couple stanzas just describing their beauty.  Their bright, happy existence is of great comfort to Wordsworth, and heals him from his loneliness:

"A poet could not but be gay,
In such a jocund company:
I gazed---and gazed---but little thought
What wealth the show to me had brought:

For oft, when on my couch I lie
In vacant or in pensive mood,
They flash upon that inward eye
Which is the bliss of solitude;
And then my heart with pleasure fills,
And dances with the daffodils."

So, he states in the above stanzas, who could NOT be happy gazing upon these flowers?  That sight brought him great "wealth" (not literal, but figurative wealth in the form of happiness and joy).  He goes on to state that whenever he is lying about feeling empty or moody, he remembers that sight, and how those daffodils were completely blissful to be alone on that hill, and it fills his heart with pleasure and makes it dance.  So, nature, for Wordsworth, is very much a healer.  He saw a field of flowers once, and he calls upon that image whenever he feels distraught, and that image of nature alone heals him of his "vacant" and "pensive" mood.  It is a theme in much of Wordsworth's poetry, and if you have ever been up in the mountains, or on a hike in the woods and felt the serenity that exists in nature, it is easy to understand how he took such comfort in it.