Here's the actual source -- which doesn't have the precise wording I remember so clearly, but near enough.
God Needs Antonio
Your soul was lifted by the wings today
Hearing the master of the violin:
You praised him, praised the great Sabastian too
Who made that fine Chaconne; but did you think
Of old Antonio Stradivari? -him
Who a good century and a half ago
Put his true work in that brown instrument
And by the nice adjustment of its frame
Gave it responsive life, continuous
With the master's finger-tips and perfected
Like them by delicate rectitude of use.
That plain white-aproned man, who stood at work
Patient and accurate full fourscore years,
Cherished his sight and touch by temperance,
And since keen sense is love of perfectness
Made perfect violins, the needed paths
For inspiration and high mastery.
No simpler man than he; he never cried,
"why was I born to this monotonous task
Of making violins?" or flung them down
To suit with hurling act well-hurled curse
At labor on such perishable stuff.
Hence neighbors in Cremona held him dull,
Called him a slave, a mill-horse, a machine.
Naldo, a painter of eclectic school,
Knowing all tricks of style at thirty-one,
And weary of them, while Antonio
At sixty-nine wrought placidly his best,
Making the violin you heard today -
Naldo would tease him oft to tell his aims.
"Perhaps thou hast some pleasant vice to feed -
the love of louis d'ors in heaps of four,
Each violin a heap - I've naught to blame;
My vices waste such heaps. But then, why work
With painful nicety?"
"I like the gold - well, yes - but not for meals.
And as my stomach, so my eye and hand,
And inward sense that works along with both,
Have hunger that can never feed on coin.
Who draws a line and satisfies his soul,
Making it crooked where it should be straight?
Antonio Stradivari has an eye
That winces at false work and loves the true."
Then Naldo: "'Tis a petty kind of fame
At best, that comes of making violins;
And saves no masses, either. Thou wilt go
To purgatory none the less."
"'Twere purgatory here to make them ill;
And for my fame - when any master holds
'Twixt chin and hand a violin of mine,
He will be glad that Stradivari lived,
Made violins, and made them of the best.
The masters only know whose work is good:
They will choose mine, and while God gives them skill
I give them instruments to play upon,
God choosing me to help him.
"What! Were God
at fault for violins, thou absent?"
He were at fault for Stradivari's work."
"Why, many hold Giuseppe's violins
As good as thine."
"May be: they are different.
His quality declines: he spoils his hand
With over-drinking. But were his the best,
He could not work for two. My work is mine,
And, heresy or not, if my hand slacked
I should rob God - since his is fullest good -
Leaving a blank instead of violins.
I say, not God himself can make man's best
Without best men to help him.
'Tis God gives skill,
But not without men's hands: he could not make
Antonio Stradivari's violins
Without Antonio. Get thee to thy easel."
-- George Eliot