You would be justified in regarding statement contained within the secondary title above with a certain degree of skepticism. After all, poetry and lyrics do bear some striking superficial similarities. Both are often rhymed. Both are often rhythmic. Both can achieve an elegance virtually unmatched in prose.
The problem is that there the similarities stop. Once you begin looking at concrete examples, any claim of equivalency between the two forms instantly deflates. Let us take for our example one of the most well-known poems in the American repertoire: Robert Frost’s “The Road Not Taken.”
Two roads diverged in a yellow wood,
And sorry I could not travel both
And be one traveler, long I stood
And looked down one as far as I could
To where it bent in the undergrowth.
Then took the other, as just as fair,
And having perhaps the better claim,
Because it was grassy and wanted wear;
Though as for that the passing there
Had worn them really about the same.
And both that morning equally lay
In leaves no step had trodden black.
Oh, I kept the first for another day!
Yet knowing how way leads on to way,
I doubted if I should ever come back.
I shall be telling this with a sigh
Somewhere ages and ages hence:
Two roads diverged in a wood, and I–
I took the one less traveled by,
And that has made all the difference.
A lovely poem, I think you will agree, but try writing a melody for it. Rhythmically, of course, it is possible to do so, but tonally it is impracticable. Try setting the poem’s ending to music; you will fail miserably. Like much of Frost’s poetry, it relies on stark understatement for its effect. Adding music would be, at best, an egregious redundancy. It does nothing for the poem that the poem does not already do for itself, and better.
But there is a more fundamental difference at work here. Poetry, by and large, is intended to be read. In revealing its meaning it burns slowly. The poet is permitted to be elusive and even vague, safe in the knowledge that the reader will be able to read a troublesome line repeatedly and eventually divine its meaning. The lyricist does not have this luxury. Lyrics are a much more immediate art form by virtue of being almost exclusively heard rather than read. When you only have one shot at communicating your meaning to an audience, you had damn well better say what you want to and say it clearly.
So there is a divide in the required level of clarity in either form, but I would also argue that on a more fundamental level, while poetry is predominately an independent art form, lyrics must by definition be collaborative. Lyrics are not meant to stand alone, nor should that be your goal as a lyricist. The lyrics and the music must combine to create a whole that is greater than the sum of its parts. Neither side is at the mercy of the other; rather, the relationship is markedly symbiotic. Each complements and improves the other, and far from rejecting the notion of lyrics as art, this fact affirms it. The measure of a great poet is in the words alone, but the measure of a great lyricist lies in how entirely the words are wrapped up with the music. It is this symbiosis that defines and establishes lyrics as their own artistic entity.