Analysis of The Test

I hung my verses in the wind,
Time and tide their faults may find.
All were winnowed through and through,
Five lines lasted sound and true;
Five were smelted in a pot
Than the South more fierce and hot;
These the siroc could not melt,
Fire their fiercer flaming felt,
And the meaning was more white
Than July's meridian light.
Sunshine cannot bleach the snow,
Nor time unmake what poets know.
Have you eyes to find the five
Which five hundred did survive?