You will be secure ... will find safety ... will take your rest in safety

Zophar repeats the idea to emphasize how safe Job will be. Job will experience this if he does what Zopahr spoke of in verses 13 and 14.

will take your rest in safety

"Take your rest" here is an idiom for "rest." The phrase "in safety" can be expressed with the word "safely." Alternate translation: "will rest safely" (See: rc://en/ta/man/translate/figs-idiom and rc://en/ta/man/translate/figs-abstractnouns)