So it came about when Moses held his hand up, that Israel prevailed, and when he let his hand down, Amalek prevailed. But Moses’ hands were heavy. Then they took a stone and put it under him, and he sat on it; and Aaron and Hur supported his hands, one on one side and one on the other. Thus his hands were steady until the sun set. (Exodus 17:11-12)
Moses grew weary, and then his friends assisted him. When at any time your prayer flags, let faith support one hand, and let holy hope uplift the other, and prayer seating itself upon the stone of Israel, the rock of our salvation, will persevere and prevail. Beware of faintness in devotion; if Moses felt it, who can escape? It is far easier to fight with sin in public, than to pray against it in private. It is remarked that Joshua never grew weary in the fighting, but Moses did grow weary in the praying; the more spiritual an exercise, the more difficult it is for flesh and blood to maintain it. Let us cry, then, for special strength, and may the Spirit of God, who helpeth our infirmities, as he allowed help to Moses, enable us like him to continue with our hands steady “until the going down of the sun;” till the evening of life is over; till we shall come to the rising of a better sun in the land where prayer is swallowed up in praise.
From Charles Spurgeon Morning and Evening Devotional