Drayton's speaker never speaks to his beloved here. He speaks to a river. The Anker is greeted in the first word as "Clear," then treated as witness, messenger and finally source of inspiration. The central idea is that love for a woman and love for a place have become one feeling, and that this ordinary stretch of English water deserves a place beside the famous sacred sites of the classical world.
The opening quatrain makes the lady and the landscape inseparable. Idea, as the poem calls her, "lies" on the Anker's shore, and the verb is pleasantly slippery: she may be resting, dwelling, or simply belonging there. The language around her is devotional. She is a "soul-shrin'd saint," the swans "adore" the stream, and the brook is "blessed." Most striking is the claim that the water is "refined by her eyes." Her gaze purifies it, as if she were an alchemist's stone. That explains the river's opening epithet: it is clear because she has looked at it. The compliment goes to her, and the river simply receives it.
The second quatrain keeps the scenery lavish. Zephyr, the west wind, "distils his nectar-dropping showers," and nightingales sing among "dew-impearled flowers." Notice how many of the words are hyphenated compounds: "silver-sanded," "milk-white," "myrrh-breathing," "nectar-dropping," "dew-impearled." Each squeezes a whole sensory picture into one phrase, and almost all of them borrow from luxury goods or divine food: silver, pearls, myrrh, nectar. The Arden of this poem is not a muddy Midlands woodland but a jewel-box, with sight, smell, touch and sound all present within eight lines. Rain becomes a distilled perfume, which echoes the alchemical hint of "refined" earlier.
At line nine the poem turns. "Say thus, fair Brook" changes description into instruction, and the third quatrain is a little speech in quotation marks, a poem within the poem. The river is to tell "thy Queen" that her "shepherd spent his wand'ring years" here and "sacrific'd his tears." Three roles are given to the woman in quick succession: saint, queen, and "dear nymph." Each comes from a different tradition, religious, courtly and pastoral, and the speaker adopts the matching role himself: worshipper, subject and shepherd. His tears become a ritual offering, so grief is given dignity. The past tense ("spent," "hath been") also suggests a man looking back over a long devotion, which sits oddly against the sunny scene and gives the sweetness a faint ache.
Formally the poem is a Shakespearean sonnet, rhyming abab cdcd efef gg, in a steady iambic pentameter. The rhymes are simple and open (shore/adore, Spring/sing, been/Queen), and the lines mostly end where a phrase ends, so the poem moves with the unhurried calm of the water it describes. Nothing jolts, which suits a speaker who wants to sound courteous rather than desperate.
The couplet is where the poem shows its ambition: "Fair Arden, thou my Tempe art alone, / And thou, sweet Anker, art my Helicon." Tempe was a famously beautiful valley in Greece, and Helicon was the mountain of the Muses, whose springs were linked with poetic inspiration. By naming them, Drayton makes the earlier classical touches (Zephyr, nectar, nymph) pay off. He has been dressing Warwickshire in Greek costume only to announce that he needs no Greece at all. "Alone" is the key word: Arden is not like Tempe, it is the only Tempe he wants. The Anker is not only a pretty setting but the spring his poetry drinks from, so the sonnet quietly thanks the thing that made it possible.
That is where its significance lies. The sonnet takes a tradition that usually looks to Italy and Greece and roots it in a local river, claiming that English places can carry the same poetic weight as ancient ones. The praise is highly conventional, and the river is hardly described as a real stream, but the poem's charm lies in its confidence. A speaker who can hail a brook as his Helicon is a poet who believes inspiration is close at hand.