The Old Testament is undoubtedly fundamentally different to the new especially when it comes to the nature of God, in the Old Testament God orders the murder of men, of women and of children but in the New Testament he comes across as a more loving, kind and forgiving, but how should Christians approach or view the ethnics and morality of the Old Testament?
This question will probably be closed, but I'd like to provide a meta-answer that the way you approach the ethics of the Old Testament is with integrity and honesty.
It's not the case that post-enlightenment humanistic ethics are compatible with the scriptures. They're just not. Moreover the Bible is very clear that they are not. E.g. that God's ways are not man's ways, and that God judges differently than man. That the mind of man is at enmity with God. That God did not want man to judge good and evil.
So why not take all those passages at face value? Attempts to look at the mass killings in the Bible and try to make them palatable to the carnal (human) mind will go down two paths
- The people who were killed deserved to die because they were bad from the view of the human mind
- God didn't really kill them, Satan did.
These don't meet basic honesty tests. It's hard, for example, to justify all the children and animals killed in Noah's flood or the deaths of the firstborn in Egypt in terms of people being guilty according to the natural mind, as infants are considered innocent by most people, and that's a lot of infants. Similarly saying God didn't want to do it or really it was Satan that sent that Angel of Destruction or Satan that opened up the waters of the heavens leads to a poor reading of the texts.
I think you must face these issues with integrity and honesty. You can conclude that your sense of morality is wrong, or that God is wrong, or that the text is wrong. That then is a personal decision and now we get into theological debates.
But I do think that this is an important topic because it's an example where there is a great temptation to change the meaning of the text in order to meet your sense of morality so this is the canonical test of doing honest hermeneutics.