My lips shall not speak wickedness - This solemn profession made on oath might have done something to allay the suspicions of his friends in regard to 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 countenance error or to palliate 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.

My lips shall not speak wickedness - As I have hitherto lived in all good conscience before God, as he knoweth, so will I continue to live.

(b) My lips shall not speak wickedness, nor my tongue utter deceit.
(b) However men judge me, yet will I not speak contrary to that which I have said, and so do wickedly in betraying the truth.

My lips shall not speak wickedness,.... This is the thing he swears to, this the matter of his oath, not only that he would not speak a wicked word not anything corrupt, unsavoury, unchaste, profane, and idle nor speak evil of his neighbours and friends or of any man; but that he would not speak wickedly of himself, as he must do, if he owned himself to be a wicked man and an hypocrite as his friends charged him, and they would have had him confessed; but he swears he would not utter such wickedness as long as he had any breath in him:
nor my tongue utter deceit; which respects the same thing; not merely any fallacy or lie, or what might impose upon and deceive another, which yet he was careful of; but such deceit and falsehood as would be a belying himself, which would be the case should he say that he was devoid of integrity and sincerity.

(Job 6:28, Job 6:30). The "deceit" would be if he were to admit guilt against the witness of his conscience.