"Home-Thoughts, from Abroad" begins with a wistful sigh. "Oh, to be in England," the speaker says, "Now that April's there." Far from home, this speaker is terribly homesick—especially now that it's springtime. In fact, to this speaker, it seems to be April only "there," in England: wherever they are now, April just doesn't feel the same.
In these first four lines, the speaker is getting caught up in a reverie, their thoughts carrying them far away from the foreign country where they sit now. What especially catches the speaker's fancy is the morning "whoever wakes in England" looks out their window to see that spring has arrived for real. This poem will capture, not just the speaker's longing for home, but the pure joy of spring renewal.
Take a look at the way the structure of these first lines captures the speaker's yearning:
Oh, to be in England
Now that April's there,
And whoever wakes in England
Sees, || some morning, || unaware,
The diacope on "in England" here (strengthened by enjambments that leave those words prominent at the ends of lines) makes it feel like the speaker's mind is being drawn back, over and over, to their beloved home.
The caesurae in line 4 create breathy pauses—as if the speaker is anticipating a surprise, barely able to contain their delight. "Whoever wakes in England," that changed rhythm suggests, has no idea of all the beauty that's about to hit them when they draw the curtains "some morning."