Albert Barnes Commentary Job 20:13

"Though he spare it, and will not let it go, But keep it still within his mouth;" — Job 20:13 (ASV)

Though he spare it — That is, though he retains it long in his mouth, that he may enjoy it the more.

And forsake it not — Retains it as long as he can.

But keep it still within his mouth — Margin, as in Hebrew “in the midst of his palate.” He seeks to enjoy it as long as possible.