"And what!" he says, "is it a mortal who blames me?" that is, no mortal can blame me. I am not fighting against a man.
Source: COMMENTARY ON JOB 21:3-6
Job 21:4
4 As for me, is my complaint to man? and if it were so, why should not my spirit be troubled?
Commentaries
Ver. 4. As for me, is my dispute against man, that I should not be justly sad?
42. Whosoever in pleasing God displeases man, has no grounds for sadness. But he, who in pleasing man displeases God, or thinks that he displeases both God and man together, if sadness does not come upon him, proves a stranger to the excellency of wisdom. Now blessed Job believed that he had displeased God in the midst of his strokes, and therefore he called back his mind to sadness, in that He was not to be disregarded, Whom he was afraid that he had displeased. Now, if he had been pleading against man concerning the merits of his life, he would have had no occasion to feel sadness, but seeing that by his present strokes he was made doubtful of his past life, he justly sought for sadness under the scourge.
42. Whosoever in pleasing God displeases man, has no grounds for sadness. But he, who in pleasing man displeases God, or thinks that he displeases both God and man together, if sadness does not come upon him, proves a stranger to the excellency of wisdom. Now blessed Job believed that he had displeased God in the midst of his strokes, and therefore he called back his mind to sadness, in that He was not to be disregarded, Whom he was afraid that he had displeased. Now, if he had been pleading against man concerning the merits of his life, he would have had no occasion to feel sadness, but seeing that by his present strokes he was made doubtful of his past life, he justly sought for sadness under the scourge.
Lest his words will be necessarily condemned, he shows that he is about to speak the great matters of divine judgment and not human judgments. Thus he says, "Is my debate against a man so that I should not be sad with merit?", as if to say: If the intention of my argument was to question whether a man justly or unjustly afflicted me, in whatever way this happened, I would lack sadness with reason. But my intention is to inquire how this has happened by the just judgment of God.
Source: Commentary on Job