What we see when God was establishing the nation of Israel is quite different than what we see in the NT. Many things that God did and told people to do are relevant, even prophetic in substance.
Abraham being willing to sacrifice his own son and his son was willingly obedient to his father and the replacement of the ram for a sacrificial blood offering. They are all prophetic, an image of future events. So they had more than one purpose in God's plan.
God did not tell Moses to murder anyone that I know of. The three thousand who lost their lives at Mt Sinai were judged by God as idolators and their sentence of death was carried out by those who were not idolators. But in the NT we don't see any teachings that say we are to kill someone for idolatry. In fact, on the day of Pentecost rather than people dying 3,000 people were saved.
God commanded the Israelites to claim the land of Canaan and how to go about it. God knowing all things knew the hearts of the Canaanites. When God told them to destroy the Amalekites they didn't and the Amalekites would continue in their generations to harm the people of the nation of Israel. We don't see God commanding these types of things in the NT dispensation that we are living in. God is among all the nations now, not just the nation of Israel.