ABC:Deuteronomy 23

Verse 3, Who to Convert?
Patheos' Bob Seidensticker claims there is a contradiction here and makes the following comments (italicized):

Who should the disciples convert? At the end of the gospel story, Jesus has risen and is giving the disciples their final instructions. Matthew 28:19 Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: This is the familiar Great Commission, and it’s a lot more generous than what has been called the lesser commission that appears earlier in the same gospel:  Matthew 10:5-6 ¶ These twelve Jesus sent forth, and commanded them, saying, Go not into the way of the Gentiles, and into any city of the Samaritans enter ye not: But go rather to the lost sheep of the house of Israel. This was not a universal message. We see it again in his encounter with the Canaanite woman: Matthew 15:24-26 But he answered and said, I am not sent but unto the lost sheep of the house of Israel. Then came she and worshipped him, saying, Lord, help me. But he answered and said, It is not meet to take the children's bread, and to cast it to dogs. You might say that a ministry with limited resources had to prioritize, but that doesn’t apply here. Don’t forget that Jesus was omnipotent. Going back to the Old Testament, we don’t find an all-inclusive message there, either. The Israelites were God’s “Chosen People,” and God had harsh things to say about neighboring tribes. Deuteronomy 23:3 An Ammonite or Moabite shall not enter into the congregation of the LORD; even to their tenth generation shall they not enter into the congregation of the LORD for ever: God also forbids intermarriage with these foreign tribes (Deut. 7:3; Ezra 9:2, 10:10; Nehemiah 13). Let’s revisit the fact that Matthew is contradictory when it says both “Make disciples of all nations” and “Do not go among the Gentiles [but only] to the lost sheep of Israel.” There are no early papyrus copies of Matthew 28 (the “Make disciples of all nations” chapter), and the earliest copies of this chapter are in the codices copied in the mid-300s. That’s almost three centuries of silence from original to our best copies, a lot of opportunity for the Great Commission to get “improved” by copyists. I’m not saying it was, of course; I’m simply offering one explanation for why the gospel in Matthew has Jesus change so fundamental a tenet as who he came to save.

There is no contradiction here, just a critic ignoring chronology and context. Because of the promises to Abraham, Isaac, and Jacob, it was necessary that the Gospel had to first be delivered to the Jews; only after rejecting it was it made available to the Gentiles. (Acts 3:25-26; 13:46; Luke 24:47) Nonetheless, it was not God's will that this should cause the downfall of the Jews, but that their rejection would lead to mercy for the Gentiles, who by then showing mercy to the Jews and preaching the Gospel to them, God might have mercy upon all. (Romans 11:30-32)

As such, the disciples were originally sent to the Jews specifically (Matthew 10:5-6) but Jesus then gradually showed them that His salvation would also be to the Gentiles (Matthew 15:24-28); culminating in the Great Commission telling them to witness to all nations. (Matthew 28:19) When the disciples try to send the Canaanite woman away, Jesus refuses, telling them that He's not sent only to the House of Israel. (Matthew 15:24) He then uses the situation to show mercy on her, healing her daughter because of her faith, verses that the critic dishonestly omits. (Matthew 15:27-28) Jesus continued to heal and preach to the Gentiles, (Luke 17:16; John 4:9-42) while using parables to teach against the long-held Jewish biases against the Gentiles. (Luke 10:33-36)

With the Ammonites and Moabites, they were kept from becoming Israelites because as a nation they had persecuted the Israelites, refusing them food and water while hiring Balaam to curse them. (Deuteronomy 23:3-4; Nehemiah 13:1-2) The critic once again omits the explanatory verses which provide context. However, foreigners/Gentiles in general could become Israelites, as Rahab and Ruth did (Joshua 6:25; Ruth 1:16; Matthew 1:5), by entering Israel and adopting Israelite practices. (Exodus 12:48; Numbers 9:14; Deuteronomy 31:12) Indeed, there were numerous commandments by God prohibiting discrimination against these foreigners/immigrants dwelling in Israel (KJV strangers) since Israel had themselves been immigrants oppressed in the land of Egypt, requiring that they be treated fairly like Israelites and allowed to harvest food when they needed it. (Exodus 12:49; 20:10; 22:21; 23:9; Leviticus 19:10,33-34; 23:22; 24:22; 25:6; Numbers 9:14; 15:15-16; Deuteronomy 1:16; 5:14; 10:18-19; 14:29; 16:11,14; 23:7; 24:17,19-21; 26:11-13; 27:19) Jesus in the New Testament states that how others treat them will be used as a basis for God's judgment at the Final Judgment. (Matthew 23:35,38,43)

Intermarriage into Canaanite nations specifically was forbidden to prevent Israelites from adopting their practices, such as cannibalistic child sacrifice to idols like Baal and Molech. (Deuteronomy 12:31; Exodus 34:12-16) See Destruction of Canaanites. However, again, members of those nations could become Israelites by abandoning their pagan practices and becoming Israelite citizens. When Aaron and Miriam discriminated against Moses' Ethiopian wife because of her skin color, God ironically punished Miriam by giving her leprosy so that her skin turned white, forcing her to live in exile for a week as punishment. (Numbers 12) In Song of Solomon 1:6, we are specifically commanded against judging others based on dark skin, and told that it is caused by exposure to the sun. See Dawkins' Criticisms for what the Bible teaches about racism.

As for Matthew 28, it is quoted by numerous church fathers well before 300 A.D., including Ignatius, Tertullian, and Hippolytus, as pointed out by J.P. Holding of Tektonics.