Exodus 17:10-13 So Joshua did as Moses had said to him, and fought with Amalek: and Moses, Aaron, and Hur went up to the top of the hill. (11) And it came to pass, when Moses held up his hand, that Israel prevailed: and when he let down his hand, Amalek prevailed. (12) But Moses' hands were heavy; and they took a stone, and put it under him, and he sat thereon; and Aaron and Hur stayed up his hands, the one on the one side, and the other on the other side; and his hands were steady until the going down of the sun. (13) And Joshua discomfited Amalek and his people with the edge of the sword.
This passage comes immediately after the account of the Lord's producing the water from the rock. We've already seen how the rock typified Christ. This theme runs consistently throughout the Bible. It has been said that Amalek could represent our sin nature which is not removed when we are saved, but it should be dormant, so to speak. "Let not sin therefore reign in your mortal body, that ye should obey it in the lusts thereof." (Romans 6:12) If that is true and we follow the model, we notice that Moses was able to produce a superficial victory for a period of time, but eventually he became fatigued and dropped his hands, and Amalek prevailed (the sin nature becomes active when we trust in anything but Christ and Him crucified).
But look at the solution. Moses sat upon a stone. Figuratively speaking, he was resting upon Christ, the Rock of his salvation. Aaron, Israel's first high priest, held up one of Moses' hands; he can easily be seen to represent our High Priest, Jesus Christ. The other hand was held by Hur, which some have said could represent the Holy Spirit. (I'm not sure how they come to this conclusion, but it would be consistent with the model.) Notice that in this situation, Moses is doing absolutely no work. He is simply submitting to the help of all involved. Of course he could refuse the help and try to do it on his own, but the result would eventually be defeat.
Let us learn this important lesson. We must always rest on the fact of Christ's finished work on the cross. Anytime we depend on our own efforts, the result is failure.
For he that is entered into his rest, he also hath ceased from his own works, as God did from his. Let us labour therefore to enter into that rest, lest any man fall after the same example of unbelief. (Hebrews 4:10-11)