There are twenty lines and every line rhymes with at least one other line. Five rhymes are used. Trace the rhyming pattern of the poem.

In my craft or sullen arta
Exercised in the still nightb
When only the moon ragesc
And the lovers lie abedd
With all their griefs in their arms,e
I labour by singing lightb
Not for ambition or breadd
Or the strut and trade of charmse
On the ivory stagesc
But for the common wagesc
Of their most secret heart.a

Not for the proud man aparta
From the raging moon I writeb
On these spindrift pagesc
Nor for the towering deadd
With their nightingales and psalmse
But for the lovers, their armse
Round the griefs of the ages,c
Who pay no praise or wagesc
Nor heed my craft or art.a

Use a for the first line rhyme, b for the second line rhyme etc. up to e for line 5, then put the letter against the appropriate rhyming words of subsequent lines.
How far does the rhyming that is here add to the poem?