The poem opens with the song of the Clod (a small clump of earth or clay). In this song, the clod presents its vision of love, which is characterized by a kind of extreme selflessness. Love doesn't require or desire anything, according to the humble Clod, nor does it even have "any care" for itself at all. In other words, love is all about generosity and sacrifice.
As is often the case with Blake's poems, the simple and sparse language here masks complex ideas. First, there are multiple layers of personification at work here: the Clod is personified—given a voice—and the Clod in turn personifies love.
Love itself is portrayed as capable of selflessness or selfishness. This "Love" might refer specifically to the way that people love each other, but it could also refer to love as a kind of force—the expression of God, perhaps.
It's important to keep in mind Blake's strong commitment to the Christian faith (though his views on Christianity were fiercely independent). To that end, the Clod's definition of love aligns closely with typical Christian ideas. God gave the world his son, Jesus, as a kind of loving sacrifice (who, in turn, sacrificed himself for humanity). As the Clod seems to express, people should show a similar willingness to love—and sacrifice—without the expectation of reward.
The sound of the opening lines is very gentle, supporting the idea of love as self-sacrifice. The soft /th/ sounds in "seeketh" and "hath," combined with the sibilance running throughout the lines, grant the lines a hushed quiet—as though the poem itself is submitting to another authority.
These lines also establish the poem's meter of iambic tetrameter, four poetic feet per line in an ustressed-stressed syllable pattern:
"Love seeketh not itself to please,
Nor for itself hath any care,
These lines aren't necessarily perfect in their meter—it's possible to stress the opening word "Love," for example, as we've done here—but they are relatively steady and familiar in their sound.