Preparing for war is necessary for any nation. God needed to give rules for the conduct of war to the new nation of Israel. There are principles in Deuteronomy 20 which can help us in our battles too.

As a new nation, Israel had no time to build a fully equipped army. Yet, they were required to go to war with enemies that were likely to have far superior military power (v. 1). The solution? Trust God for victory (vv. 1-4). He acted on their behalf in bringing them ″up out of Egypt″ (v. 1), and these actions of God gave powerful testimony to His ability to help the people face any challenge. The history of God's dealings with people encourages believers to face challenges with confidence.

The next piece of advice had to do with the role of priests in the battles. They were to ″come forward and address the army″, reminding them not to fear and to remember that God was with them (vv. 2-4). The priests were not experts at war, but they knew the ways of God. They could apply God's truth to the challenge the people faced. Military and school chaplains perform a similar role today, as do Christian leaders who encourage those going into crucial ″battles″, like a risky surgery, an important exam, or a job interview. They can encourage hope and perseverance through a visit, a prayer meeting, or a phone call.

Then, in verses 5-8, after the rousing call to arms, there is a deliberate trimming of the troops. Because this is the Lord's battle, size is not a problem. Army officers are instructed to trim their troops by dismissing those who had special family responsibilities. We sometimes admire the commitment of people whose families suffer because of their work. But trust in God during a massive project includes caring for family. Ministries and Christian employers must not let workers' families suffer because of their work.

Next, Moses says that those who are timid should not join the army to go to battle. Their negativity can demoralise others and this can pose a huge problem in a time of war. Therefore, provision is made for those who are ″afraid or fainthearted″ to ″go home″ (v. 8). We need to give special attention to people who show signs of debilitating discouragement during our urgent projects.

Lastly, wars cannot be won without proper organisation. A leader must direct the team's activities. So, commanders are appointed over the army (v. 9).

The next few verses (vv. 10-18) are so specific to Israel's wars that we will not make many applications from them to our life in the present. But there's an interesting instruction in verse 19 that warrants our attention.

The chapter closes with the prohibition of cutting down trees which bear edible fruit. We battle against human opponents in war, not against morally neutral vegetation (v. 19). Long before the development of ″green theology″, Deuteronomy advocates the conservation of trees, even though military powers of the time showed no concern for this.