John Gill

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 Psa 69:10. And my flesh faileth of fatness; or "for want of oil" (k); the radical moisture of his flesh being dried up like a potsherd, Psa 22:15. (k) , Sept. "propter oleum", V. L. "propter defectum olei", Eth. Arab.