How many sentences are there in this poem? What is the main verb in each sentence? What tense are these main verbs in? Can you suggest a reason for this choice?

In my craft or sullen art
Exercised in the still night
When only the moon rages
And the lovers lie abed
With all their griefs in their arms,
I labour by singing light
Not for ambition or bread
Or the strut and trade of charms
On the ivory stages
But for the common wages
Of their most secret heart.

Not for the proud man apart
From the raging moon I write
On these spindrift pages
Nor for the towering dead
With their nightingales and psalms
But for the lovers, their arms
Round the griefs of the ages,
Who pay no praise or wages
Nor heed my craft or art.

Are you sure that is the most important verb?
Are you sure that is the main verb? Does it relate to the main grammatical subject of the sentence?
What is the writer doing at the ‘present moment’ when writing these lines?