To the early church fathers, the prayer of Moses in the battle with the Amalekites foreshadowed the victory Christ won on the cross. Like Aaron and Hur, we have an opportunity to stand with Christ, interceding for the salvation of souls. Of course, Moses, Aaron, and Hur had an advantage that we do not: They could see the effects of Moses’ intercession on the battle raging below. How our prayer life would change if God gave us the ability to see the effect our intercessions—or lack thereof—have on the battle that is being waged daily for souls.
The letter to the Hebrews draws a strong connection between the cross and prayer. Because every moment of our earthly existence is threatened by death, and we know neither the day nor the hour when that existence will come to an end, we, too, need to cry out to the God who can save us. Like Moses, we need the help of our fellow Christians to hold up our arms when they grow tired. We, too, need the help of the Holy Spirit to make up for what is lacking in our prayer.
The Power of the Cross by Michael Dubruiel . The book is available here in pdf version.