Job 27:4, "surely my lips shall not speak unrighteousness, neither shall my tongue utter deceit," expresses Job's firm commitment to truthfulness and righteousness in his speech, even amidst his immense suffering. Let's break it down:

"Surely my lips shall not speak unrighteousness": This means Job is determined not to utter anything that is morally wrong, unjust, or unfair. He vows to avoid falsehoods or words that would distort justice.

"Neither shall my tongue utter deceit": This reinforces the previous statement. "Deceit" refers to intentional misleading, lying, or speaking with the intention to deceive or trick others. He promises not to use his tongue to mislead or trick people.

In context: Job is defending his integrity against the accusations of his friends, who believe his suffering is a direct consequence of his sin. They try to persuade him to confess wrongdoing. This verse emphasizes his insistence that he has maintained his righteousness, and he won't abandon his conviction by falsely admitting guilt just to appease them or to find a quick solution to his problems. He refuses to speak falsely, even if it might seem like a way to alleviate his suffering.
Job is essentially stating that while he may not understand why he is suffering, he is confident in his how he has lived and continues to live his life. He will continue to speak truthfully and righteously.

Significance:

Integrity: It showcases Job's unwavering commitment to integrity, even in the face of extreme adversity. He refuses to compromise his values.
Defense Against Accusations: It's a strong rebuttal to his friends' insinuations that he's hiding sin.
Moral Strength: It highlights Job's moral strength and determination to remain true to himself and his beliefs.

The verse speaks to the importance of honesty, especially when under pressure or facing difficult circumstances. It is about maintaining moral principles and refusing to compromise one's integrity for convenience or relief.