Let's break it down:
* ABAB: The first four lines rhyme: "proud" (A), "shroud" (B), "dust" (A), "trust" (B).
* CDCD: The next four lines follow the same pattern: "foe" (C), "go" (D), "below" (C), "know" (D).
* EFEF: This continues for the following four lines: "thee" (E), "be" (F), "sleep" (E), "deep" (F).
* GG: The final two lines rhyme: "rest" (G), "best" (G).
This consistent ABAB CDCD EFEF GG pattern throughout the entire poem creates a strong sense of structure and order, which is a stark contrast to the chaotic and unsettling subject matter of death.