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.

My knees are weak through fasting - That hunger is as soon felt in weakening the knees, as in producing an uneasy sensation in the stomach, is known by all who have ever felt it. Writers in all countries have referred to this effect of hunger. Thus Tryphioderus Il. Excid. ver 155:

Τειρομενου βαρυθειεν ατερπεΐ γουνατα λιμῳ.

"Their knees might fail, by hunger's force subdued;

And sink, unable to sustain their load."

Merrick.

So Plautus, Curcul, act. ii., scen. 3: -

Tenebrae oboriuntur, genua inedia succidunt.

"My eyes grow dim; my knees are weak with hunger."

And Lucretius, lib. 4: ver. 950: -

Brachia, palpebraeque cadunt, poplitesque procumbunt.

"The arms, the eyelids fall; the knees give way."

Both the knees and the sight are particularly affected by hunger.

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 Psalm 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, Psalm 22:15.

(k) , Sept. "propter oleum", V. L. "propter defectum olei", Eth. Arab.

My knees are weak through fasting; and my flesh {n} faileth of fatness.

(n) For hunger that came from sorrow, he was lean and his natural moisture failed him.

24, 25. Taunts and reproaches aggravate his afflicted and feeble state (Ps 22:6, 7).

109:21-31 The psalmist takes God's comforts to himself, but in a very humble manner. He was troubled in mind. His body was wasted, and almost worn away. But it is better to have leanness in the body, while the soul prospers and is in health, than to have leanness in the soul, while the body is feasted. He was ridiculed and reproached by his enemies. But if God bless us, we need not care who curses us; for how can they curse whom God has not cursed; nay, whom he has blessed? He pleads God's glory, and the honour of his name. Save me, not according to my merit, for I pretend to none, but according to thy-mercy. He concludes with the joy of faith, in assurance that his present conflicts would end in triumphs. Let all that suffer according to the will of God, commit the keeping of their souls to him. Jesus, unjustly put to death, and now risen again, is an Advocate and Intercessor for his people, ever ready to appear on their behalf against a corrupt world, and the great accuser.