What is the point of climax in the poem The Lady of Shalott" and how does the poem's structure affect the poem?

The climax in “The Lady of Shalott” is the moment when the Lady looks at Sir Lancelot. The pensive tone of the poem, which the poet uses to reveal the eventless life of the lady, is suddenly replaced by a tone of anticipation. The poet builds excitement from the point when the Lady expresses dissatisfaction with looking at shadows. The pace increases in the third part of the poem:
A bow shot from her bower eaves,
He rode between the barley sheaves,
The sun came dazzling thro' the leaves,
And flamed upon the brazen greaves
Of bold Sir Lancelot.
The poet creates a feeling of anticipation from this point onwards. The quick succession of events from the moment the Lady looks at the knight paves the road to calamity.