My knees are weak through fasting,..... Either voluntary or forced, through want of food or refreshment; this was verified in Christ, when he kneeled and prayed, and his sweat was as it were great drops of blood falling to the ground; see Ps 69:10.
And my flesh faileth of fatness; or "for want of oil" ; the radical moisture of his flesh being dried up like a potsherd, Ps 22:15. Nmvm di' elaion, Sept. "propter oleum", V. L. "propter defectum olei", Eth.