Moses has already reminded Israel that God was giving them the land because of the promise He made with their fathers, Genesis 12:1-3 / Deuteronomy 19:1.
However, if Israel wanted to receive God’s promises, they mustn’t trust in their own abilities, they must learn to trust in God’s ability to save them when it comes to waging war against their enemies, Deuteronomy 20:1. God promises to strengthen the hands of those who may be intimidated by the numbers and armament of horses and chariots of the enemy, Deuteronomy 20:1 / Deuteronomy 17:16.
He promises to remove all fear from their hearts when they put their faith in God, Deuteronomy 20:1, hence, God will fight for them against their enemies and save them, Romans 8:31 / 1 Peter 1:6-7. God made a promise that He would fight for the nation of Israel against all who would seek to destroy His eternal purpose with the nation, Deuteronomy 20:4. He was a God of war in reference to defending Israel, Exodus 15:3 / Joshua 6:17-19 / 1 Samuel 30:7 / 2 Chronicles 13:12 / Hosea 1:7.
It was God who fought for Israel to bring them into existence and into the land of promise, Deuteronomy 6:18-19 / Deuteronomy 7:1-2 / Deuteronomy 7:16-26 / Deuteronomy 9:1-6 / Deuteronomy 11:22-25 / Deuteronomy 12:29 / Deuteronomy 19:1 / Deuteronomy 31:3-8.
Notice that the men of the army of Israel were to keep fresh in their memories the fact that with a strong-arm God divided the Red Sea and brought Israel out of Egyptian bondage, Deuteronomy 9:1. When Israel are about to go into battle, the priest is to come forward and address the army and say, hear, Israel, today you are going into battle against your enemies but do not be fainthearted or afraid, do not panic or be terrified by them, Deuteronomy 20:2-3 / Numbers 31:6 / 1 Samuel 4:4 / 1 Samuel 4:11 / 2 Chronicles 13:12.
Keil, in his commentary, says the following.
‘This priest who accompanied the troops was raised to the highest dignity next to the high priest. The priest appeared just before the battle began and began his exhortation with the formula announced in these verses, ‘Hear, O Israel,’ etc. The function of the priest here was not like that of a chaplain found in the armed services of many nations today, he was of higher rank and spoke upon the DIRECT authority and commandment of God.’
Although the priests wouldn’t get involved with the fighting, Numbers 1:47-53, they would often go with the army of Israel to encourage them, Numbers 31:6 / 1 Samuel 4:4 / 1 Samuel 4:11 / 2 Chronicles 13:12.
We’re told that the priests say that there may be some men who weren’t ready or fit enough to fight in a battle. Some may have just built a house, Deuteronomy 20:5, planted a vineyard, Deuteronomy 20:6, or just got married, Deuteronomy 20:7 / Deuteronomy 24:5, it’s these men who were to return home to enjoy these things before death, Ecclesiastes 2:24.
There were others though, however, who would be excused from fighting because they were fearful, Deuteronomy 20:8. These were the men who could return to their homes, just in case their fear spread to the other soldiers, Judges 7:3 / Numbers 13-14 / Revelation 21:8.
When the officers have finished speaking to the army, they are to appoint commanders over it, Deuteronomy 20:9. In selecting those who would go to war, the leaders were to seek out only those who were of a strong heart with a strong faith in the fact that God would go to war with them.
We can almost imagine the scene here as the two armies come to face each other, we can imagine the enemy coming toward Israel with their horses, and chariots, Joshua 17:16 / Judges 4:3 / Judges 7:1-25 / 1 Samuel 13:5. The reality in the minds of the Israelites is surely, that they are about to die, Deuteronomy 1:21 / Deuteronomy 1:26 / 2 Timothy 2:3-4 / Revelation 2:10.
The priests now turn their attention to the cities and nations that are a great distance away, but note, these aren’t Canaanite cities. They say that Israel must first seek peace with them, Deuteronomy 20:10. If they accept and open their gates, all the people in it will be subject to forced labour and will work for them, Deuteronomy 20:11.
However, if no peace is extended, then they were to siege the city, Deuteronomy 20:12, kill every male, Deuteronomy 20:13, and take women and other spoils for themselves, Deuteronomy 20:14 / 2 Kings 6:24-33. This is how Israel are to treat all the cities that are at a distance from them and do not belong to the nations nearby, Deuteronomy 20:15.
Clarke, in his commentary, says the following, Deuteronomy 20:16.
‘These seven Canaanite nations might be received into mercy, provided they do the following.
1. Renounced their idolatry.
2. Became subject to the Jews.
3. Paid annual tribute and that it was only in case these terms were rejected, that they were not to leave alive in such a city anything that breathed, Deuteronomy 20:16.
The cities in the land which were Canaanite cities weren’t to be offered any peace, they were to be totally destroyed from the land of Canaan just in case they endanger the preservation of Israel, Deuteronomy 20:16-17 / Deuteronomy 7:1-6.
The reason for this is simply because ‘they will teach you to follow all the detestable things they do in worshiping their gods, and you will sin against the LORD your God’, Deuteronomy 20:18 / 2 Chronicles 8:7. In other words, God won’t tolerate this kind of evil behaviour, He hates it, Deuteronomy 7:26 / Deuteronomy 13:8-9.
Notice also, that Israel is commanded not to cut down all of the trees of a city when they besieged it, Deuteronomy 20:19. All fruit trees were to be preserved and it was only those trees that bore no fruit which was to be cut down in order to be used in besieging a city, Deuteronomy 20:20.