To be quite honest Jen, I think that to come to an understanding of any hard to discern passages of Scripture, especially in the Old Testament, you have to ask where Christ is in relation to what you're looking at. In Genesis you have the account of God bestowing a promise of blessing upon Abraham and his seed, which incorporates both a land promise, and a promise that his seed would be great, and through his seed all the families of the earth would be blessed. In forming this covenant with Abraham, God swore to bless those who bless Abraham and his seed, and curse those who cursed him. Obviously this then plays out through the lineage of Isaac, and then Jacob, who becomes Israel.
When Israel came out of Egypt four hundred years or so after, they were led by God into the land that had previously been promised to Abraham, Isaac and Jacob, which is when they began to come up against those who were determined to curse not bless Israel. And true to His Word, God came against their enemies. Note that it had nothing to do with Israel's own righteousness, but God's promise, and the wickedness of those nations they were facing.
1 "Hear, O Israel: You
are to cross over the Jordan today, and go in to dispossess nations greater and mightier than yourself, cities great and fortified up to heaven,
2 a people great and tall, the descendants of the Anakim, whom you know, and
of whom you heard
it said, 'Who can stand before the descendants of Anak?'
3 Therefore understand today that the LORD your God
is He who goes over before you
as a consuming fire. He will destroy them and bring them down before you; so you shall drive them out and destroy them quickly, as the LORD has said to you.
4 Do not think in your heart, after the LORD your God has cast them out before you, saying, 'Because of my righteousness the LORD has brought me in to possess this land'; but
it is because of the wickedness of these nations
that the LORD is driving them out from before you.
5 It is not because of your righteousness or the uprightness of your heart
that you go in to possess their land, but because of the wickedness of these nations
that the LORD your God drives them out from before you, and that He may fulfill the word which the LORD swore to your fathers, to Abraham, Isaac, and Jacob.
6 Therefore understand that the LORD your God is not giving you this good land to possess because of your righteousness, for you
are a stiff-necked people.
Deuteronomy 9:1-6 (NKJV)
The primary reason, as Dwight pointed out previously, is the purity of Israel. In the sense of ensuring the purity of the Messianic line, who is the true Seed of Abraham that would bring blessings upon all the nations of the earth. This is also why God so strictly commanded Israel to marry from within Israel, rather than interbreeding with those from other nations. Not that in the flesh those people were any worse or better than the Israelites, but according to the promise of God the Israelites were truly set apart from every other nation. The reason being because of the One to come from that nation. Obviously in the New Testament we now see this truth in its fullest light:
16 Now to Abraham and his Seed were the promises made. He does not say, "And to seeds," as of many, but as of one,
"And to your Seed," who is Christ.
17 And this I say,
that the law, which was four hundred and thirty years later, cannot annul the covenant that was confirmed before by God in Christ, that it should make the promise of no effect.
18 For if the inheritance
is of the law,
it is no longer of promise; but God gave
it to Abraham by promise.
19 What purpose then
does the law
serve? It was added because of transgressions, till the Seed should come to whom the promise was made;
and it was appointed through angels by the hand of a mediator.
Galatians 3:16-19 (NKJV)
26 For you are all sons of God through faith in Christ Jesus.
27 For as many of you as were baptized into Christ have put on Christ.
28 There is neither Jew nor Greek, there is neither slave nor free, there is neither male nor female; for you are all one in Christ Jesus.
29 And if you
are Christ's, then you are Abraham's seed, and heirs according to the promise.
Galatians 3:26-29 (NKJV)
It really is all about Christ, and the utter necessity of His coming into this world according to God's own Word, for the purpose of saving sinners by His own blood. And whilst I can't even contemplate the horror of those times, it was no doubt necessary and unavoidable as long as Israel's enemies refused to repent.
That's my tu'penny worth anyway.
God bless,
John