Deuteronomy 20 lays out laws concerning warfare, but this isn’t Sun Tzu. It doesn’t deal with strategies or techniques or troop organization. It begins with the priest addressing the people to fear not because God is with them. He is Immanuel. He is the Man of War that rides out and conquers the enemies of His people, just as He did to Egypt.
God offers potential soldiers three exemptions from war. If a man has not yet begun to enjoy his new house, his new vineyard, or his new wife, he is exempt from serving in the army. These three are very interesting. They are all very prominent pictures of God with His people used throughout scripture. God builds His people into a house in which His Spirit dwells. Israel is a vineyard planted and kept by God, the great Husbandmen. And, of course, Israel is the bride of Yahweh. As long as Israel is an undefiled house, a fruitful vineyard, and a faithful wife, God is with her and He fights for her.
A fourth exemption is set apart: fear. Fear is unbelief, mistrusting God. It spreads through the camp and causes many to fear and their hearts to melt. This is exactly why they had not been allowed entrance into the land forty years earlier.
The people were to offer terms of peace to non-Canaanite cities. If the city agreed, they could come under the service and oversight of the God of Israel. Otherwise, they would be destroyed. This is the same offer that John and then Jesus bring to the Jews, “repent for the kingdom of heaven is at hand.” This is a new conquest of the land. The kingdom of heaven is invading and it will prevail. Those who accept the king will be brought under the king’s protection and will serve the king, but those who refuse are dedicated to destruction by the consuming fire of God.
Israel was not to cut down fruit trees during a siege. John came saying, “even now the axe is laid to the root of the trees. Every tree therefore that does not bear good fruit is cut down and thrown into the fire.” Jesus comes to His vineyard looking for fruit. He says, “Abide in me, and I in you. As the branch cannot bear fruit by itself, unless it abides in the vine, neither can you, unless you abide in me. I am the vine; you are the branches. Whoever abides in me and I in him, he it is that bears much fruit, for apart from me you can do nothing. If anyone does not abide in me he is thrown away like a branch and withers; and the branches are gathered, thrown into the fire, and burned.”