Albert Barnes Commentary Job 27:4

"Surely my lips shall not speak unrighteousness, Neither shall my tongue utter deceit." — Job 27:4 (ASV)

My lips shall not speak wickedness - This solemn profession, made on oath, might have done something to lessen the suspicions of his friends regarding him and to show that they had been mistaken in his character. It is a solemn assurance that he did not mean to vindicate the cause of wickedness or to say one word in its favor; and that as long as he lived, he would never be found advocating it.

Nor my tongue utter deceit - I will never make any use of sophistry; I will not attempt to make “the worse appear the better reason;” I will not be the advocate of error. This had always been the aim of Job, and he now says that no circumstance should ever induce him to pursue a different course as long as he lived. Probably he means, also, as the following verse seems to imply, that no consideration should ever induce him to condone error or to excuse wrong. He would not be deterred from expressing his sentiments by any dread of opposition, or even by any respect for his friends. No friendship which he might have for them would induce him to justify what he honestly regarded as error.