The second stanza of this poem describes some of the worst and most painful or unpleasant situations Thomas could present. It refers to those who are drowning in storms at sea, those who are physically tortured, those who are mentally attacked by circumstances that destroy their sanity.
Strapped to a wheel, yet they shall not break;
Faith in their hands shall snap in two,
And the unicorn evils run them through;
In the face of all these terrible events, death still does not have the ultimate power. In the face of any horrendous occurrence, it is still nature that has the final say; referring back to the statement of the first stanza, all people will eventually become the same as each other and as the natural elements to which their bodies will eventually return.