Q:

"By the lives of all who’d come to console and assist the stricken" What does it mean?

I was reading the poem "The Miracle at Sea" by Shmuel HaNagid (translated from Hebrew by Peter Cole), and I came across a passage that really confused me. This is the second stanza of the poem:

By the lives of all who’d come
      to console and assist the stricken,
          by the life of each who came
      when I was in need and saw me panicked,

I would really appreciate it if someone could explain it to me.

A:

Your example is only part of the sentence spoken by the narrator and lacks the context and the first verse:
The context is when at sea, the narrator has seen a creature so horrible that the sight of it leaves those who see it disturbed for ever.
In the first verse the narrator asks the rhetorical question “Do people help each other?”
He does not answer the question directly but informs you indirectly that people do come and try to assist those who have been traumatised and he adds that, in particular, people have come to help him. 
By the lives of all who’d come 
to console and assist the stricken,
by the life of each who came
when I was in need and saw me panicked,
*could it be there’s never respite from anguish, that desolate land is desolate forever? *
He does this by using (as indicated by Isabel Archer) “By the lives/life of” is a mild oath (now old-fashioned or literary) used as solemn emphasis. 
Oaths are sworn in this manner by a respected person, a thing, a deity, etc.: they are not always "solemn." 
"By God! I will avenge the murder of my father!"; 
"By all that I hold dear, release my children"; 
"By the stars in heaven! There is a ship coming to save us."
 
The narrator is clearly grateful for the help that is offered but nevertheless, the help was of no use to him or, (we assume) the others.
The first four lines can be omitted: it is the fifth line, another rhetorical question, that is important. 

