This poem doesn't use a traditional form or meter, and therefore, it's written in a little thing we like to call free verse. But hold on a minute. Just because "This Hour and What Is Dead" is written in free verse doesn't mean it's totally free. There are formal devices at work here.
The poem lays out an 11-line pattern, which it repeats three times (with a slight variation the last time). There's an eight-line section that introduces a character our speaker is thinking about (his brother, his father, and God). This intro is followed by a three-line refrain that echoes the title (broken into a couplet and a one-line stanza), which gets slightly modified throughout the poem.
Those longer stanzas that introduce our characters also follow a pattern: we start with an image or description of the brother, the father, or God, and end with a simile, which begins "His love for me…"
This pattern is repeated three times. Even though the last section has only six lines in its first part, it has two lines after the refrain, so it's still eleven lines.
As it turns out, this pattern is pretty handy. It not only helps the poem build momentum, but it also helps hold together what is otherwise a fairly mysterious series of descriptions. It makes it easier for us, for example, to conclude that the dad is dead, too, without the poem's needing to take up space to tell us.
Plus, the form echoes the speaker's troubled state of mind. He lies awake, his thoughts circling around in his head, repeating themselves, disturbing his rest. And that's exactly how the poem sounds, isn't it? Like repetitive, haunting thoughts.
Maybe he should just try counting sheep.