Albert Barnes Commentary Job 16:5

"[But] I would strengthen you with my mouth, And the solace of my lips would assuage [your grief]." — Job 16:5 (ASV)

But I would strengthen you with my mouth. With what proceeds from the mouth—words.

And the moving of my lips—My speaking, implying that it would have been done in a mild, gentle, and kind manner, so that the lips would appear just to move. Others, however, have given a different interpretation. Thus, Dr. Good renders it:

“With my own mouth will I overpower you,
Till the quivering of my lips shall fall.”

But the common interpretation is to be preferred. The word rendered “moving,” ניד (nîyd), is from נוּד (nûd)—meaning “to move,” “to agitate,” and therefore denotes “motion.” It denotes here the motion of the lips when we speak. Gesenius renders it “consolation,” “comfort”—because this is expressed by a motion of the head.

Should assuage your grief—The word used here, יחשׂך (yachâśak), properly means “to hold back” or “to restrain” (Job 7:11). Here it is correctly rendered, meaning that he would hold back or check their sorrows. In other words, he would sustain them.