I'm speaking at the lunchbar at Lancaster University on the very tricky and emotionally engaging question above. This has been hard work to prepare.
I've decided to look at the slaughter of the Canaanites in Joshua 6 (which is often what people have in mind - at least implicitly - when they ask this question). The incident, which occurs with the invasion of Jericho, is thought to demonstrate God's lack of moral standards, that don't even seem to match up to our own. Nor can Christians just pass off these incidents as being inapplicable because they are recorded in the Old Testament. God is unchanging. And so a whole load of fears emerge... fears that God isn't good, fears that the Bible might stirs its readers to religious violence and so on.
Here's an outline of the path I'm going to take in responding to the charges against God from Joshua 6:
1. God's actions in judging the Canaanites as he did were unique because what he was doing in the world at the time was unique.
The land of Canaan was the backdrop for God’s model; an arena where the nations could see the blessing of a relationship with God, and a real-life picture pointing to forward to the Messiah, ultimately fulfilled in Jesus. Because the reality to which the model pointed has come, Christians are never called to take up arms and kill people in the name of God or Christianity today.
2. God alone has the right to demand the end of another’s life.
3. The Canaanites were not innocent.
As illustrated in Deuteronomy 18:9-12 and so on. Child sacrifices were amongst the detestable practices that God was judging.
4. God was not impatient in judging the Canaanites, but had given them many years to change their ways.
As shown in Genesis 15:16, and echoed for us today in 2 Peter 3:8-9. God's justice will still be done - and eventually he will bring a final judgement.
5. Escape was not impossible.
... As illustrated in the example of Rahab and her family (Joshua 6:17, 22-23). This illustrates the Lord's kindness, and points us forward towards the ultimate rescue he made for us through the cross.