This is a fascinating poem — which makes a profound point on the importance of singing in Christian worship. First, his poem “A True Hymn” begins with the observation –which any Christian has had– of singing joyfully partial lines and fragments of hymns. (The singer has created series of short phrases which he sings repeatedly):

MY Joy, my Life, my Crown !
My heart was meaning all the day,
Somewhat it fain would say,
And still it runneth muttering up and down
With only this, My Joy, my Life, my Crown !

Herbert tacitly concedes that the few lines are not great, but he then turns around and says “they may take part/Among the best in art”.  What makes the “few words” great is that the words perfectly accord with the soul:

Yet slight not those few words ;
If truly said, they may take part
Among the best in art :
The fineness which a hymn or psalm affords
Is, when the soul unto the lines accord.

Herbert is not saying that the songs of gathered worship should be poorly drafted (Herbert is one of the finest poets of the English language).  He is speaking about the joyful heart spontaneously bursting out lines. I think it would be turning Herbert on his head to argue that he would support poorly written songs as part of gathered worship.

But, we also must not make worship hang solely upon the artistry of the expression:

He who craves all the mind,
And all the soul, and strength, and time,
If the words only rhyme,
Justly complains that somewhat is behind
To make His verse, or write a hymn in kind.

Because, artistry is not alone the true measure of worship:

 

Whereas if the heart be moved,
Although the verse be somewhat scant,
God doth supply the want ;
As when the heart says, sighing to be approved,
“O, could I love !” and stops, God writeth, “Loved.”

An analogy may help here: Imagine two men who each write a letter to a young lady. One man writes without true love, without any actual desire for the woman, but he writes as well as Shakespeare. The second man writes with far less artistry, but he writes as well as his bursting heart can manage. The young lady knows the truth of both men: which man has successfully expressed love?