John Gill Commentary Job 19:5

"If indeed ye will magnify yourselves against me, And plead against me my reproach;" — Job 19:5 (ASV)

If indeed you will magnify [yourselves] against me
Look and talk big, set up themselves for great folk, and resolve to run him down; open their mouths wide against him and speak great swelling words in a blustering manner; or magnify what they called an error in him, and set it out in the worst light they could:

and plead against me my reproach ;
his affliction which he was reproached with, and was pleaded against him as an argument of his being a wicked man; if therefore they were determined to go on after this manner, and insist on this kind of proof, then he would have them take what follows.