“Lines Written in Early Spring” by William Wordsworth is a quintessential example of Romantic poetry, exhibiting several core characteristics of the movement: the exaltation of nature, the focus on emotion and the individual, and a critique of industrial or artificial society.
Here are the key characteristics of Romanticism present in the poem:

Exaltation of Nature as a Moral and Spiritual Guide
The most prominent feature is the portrayal of nature as a source of joy, moral purity, and spiritual truth.

Nature’s Joy and Harmony: The speaker observes that all elements of the natural world—the blended notes of the birds, the flowers, and the budding twigs—seem to be in a state of spontaneous bliss. He asserts his “faith that every flower / Enjoys the air it breathes” (Lines 11-12) and notes that the birds’ “least motion… It seemed a thrill of pleasure” (Lines 15-16). Nature is depicted as a unified, happy system.

The “Holy Plan”: Nature is elevated to a spiritual, almost divine level, referred to as having a “holy plan” (Line 22). This suggests that the natural world possesses a blueprint for moral existence from which humanity has strayed. The concept implies that there is an inherent order and purpose within the ecosystem, guiding the interactions among species and the balance of life. As humanity increasingly distances itself from this natural order through industrialization and environmental degradation, it raises the question of whether we can rediscover this connection. By contemplating the “holy plan,” we can begin to understand the consequences of our actions on the environment and perhaps find ways to realign ourselves with nature’s intended course, fostering a more sustainable and harmonious existence.

Connection to the Soul: The speaker feels a direct, mystical bond, stating, “To her fair works did Nature link / The human soul that through me ran” (Lines 5-6). This is the Romantic idea that communion with nature is essential for the health and vitality of the human spirit.

Emphasis on Emotion and the Inner Experience
Romanticism valued feeling and intuition over Enlightenment-era reason and logic. The poem is essentially an emotional meditation.

“Sweet Mood”: The poem begins by establishing the speaker’s emotional state, describing “that sweet mood when pleasant thoughts / Bring sad thoughts to the mind” (Lines 3-4). The speaker’s subjective experience is the central focus of the entire poem.

Intuition over Reason: The speaker relies on his personal conviction, saying “’tis my faith” (Line 11) and “I must think, do all I can” (Line 19), to conclude that the natural world feels pleasure. He doesn’t need scientific proof; his empathy and imagination are enough to discern nature’s inner life.

Focus on the Individual and the Common Man:
The poem uses a clear, simple poetic voice to capture a personal moment of contemplation, typical of Wordsworth’s style in the Lyrical Ballads.

First-Person Lyric: The use of “I” (“I heard,” “I sate,” “my heart”) makes the poem a personal lyric, centering the experience on the solitary individual observing and reflecting on his surroundings.

Simple Language: The language is intentionally straightforward and accessible, reflecting Wordsworth’s goal of using “language really used by men” and choosing subjects from “common life,” moving away from the elaborate diction of 18th-century poetry.

Critique of Society:
The harmony of nature serves as a direct contrast and critique of human society.

The Lament: The poem’s central conflict and sorrow revolve around the line that bookends the meditation: “And much it grieved my heart to think / What man has made of man” (Lines 7-8 and 23-24).

Loss of Innocence: This grief refers to the political corruption, social injustice, war, and the dehumanizing effects of the rapidly expanding Industrial Revolution. The speaker laments that humans have created a system of cruelty and suffering, effectively divorcing themselves from the natural peace enjoyed by all other creatures.