My knees are weak through fasting - Hunger; want of food. Strength to stand is connected with firmness in the knee-joints, and hence, weakness and feebleness are denoted by the giving way of the knees. Compare Hebrews 12:12.

And my flesh faileth of fatness - I am lean and weak. There is not the proper supply for my strength. The idea seems to have been that fatness (Hebrew, oil) was necessary to strength.

Continues after advertising
Continues after advertising