Why might have God confined his atonement to only the Israelites?

In the Old Testament, the nation of Israel was God’s chosen instrument for witnessing about God’s saving grace. It was in this sense that Israel became the “chosen nation” (Ex 19:5). Specifically:

• Israel was to be a kingdom of priests to teach all nations (Ex 19:5, 6, Isa 61:6).
• Israel was to be a light to the world (Isa 42:6, 49:6, 60:3).
• Israel was to be a blessing to all nations via both their spiritual example and teaching, and the promised Messiah (Gen 12:2-3; 18:18; 22:18, Ps 67:1-2, Isa 2:2-4, 55:5, 61:9-11, 66:19-20, Jer 3:17)

Note that while Israel was chosen as the instrument to tell and show the world of God’s saving grace, salvation was always available to all people. Indeed, the Old Testament contains many examples of foreigners becoming part of Israel, indicating that the Israelite Covenant was open to all and was never exclusive. For example:

• Abraham’s own household must have consisted of perhaps 2000 people just to be able to raise an army of 318 men to liberate Lot, Gen 14:14. Indeed, Abraham’s chief servant (from Damascus) was clearly a believer and very devout as shown in Gen 24.
• The unfortunate story in Gen 38 about Judah and Tamar shows that a foreigner became the mother of the tribe of Judah.
• When Jacob entered Egypt, his family numbered 75 people (Acts 7:14, Ex 1:5). Some of these were not direct descendants of Abraham such as the wives of the 12 patriarchs, notably Joseph’s own wife. 215 years and four generations later at the exodus, Israel’s army had over 600,000 men, excluding women and children, (Ex 12:37, Num 1:46, etc) suggesting a total population of several million people, requiring many additions. This included a significant mixed multitude (Ex 12:38) showing that Israel obviously consisted of many non-biological Jews had joined. (Note that it is biologically impossible for Israelite numbers to have grown from 75 to several million biologically without many outside additions.)
• Moses married a Midianite (Ex 2:16-21) also known as a Cushite. Miriam and Aaron were severely reprimanded and punished for displaying racism (Num 12:1, 2)
• Caleb, who represented and led the tribe of Judah was a Kennizite (Num 32:12).
• Rahab was a Canaanite (Josh 2:1, 2, Matt 1:5)
• Ruth was Moabite (Ruth 1:4 16, 17, Matt 1:5) – these last two make King David descended from foreigners (Ruth 4:13-16).
• Uriah was a Hittite (2 Sam 11:3)
• King David’s elite personal regiment consisted of Gittites, that is, Philistines (2 Sam 15:18-22, 1 Chron 18:17)
• Isa 56:6, 7 - And the foreigners who join themselves to the LORD to minister to Him, to love the name of the LORD, and to be His servants— all who keep the Sabbath without profaning it and who hold fast to My covenant—I will bring them to My holy mountain and make them joyful in My house of prayer. Their burnt offerings and sacrifices will be accepted on My altar, for My house will be called a house of prayer for all the nations.” See also V3.
• The Rechabites were Kenites (Jer 35:1-19)
• Many other foreigners lived in Israel (1 Chron 22:2, 17, 2 Chron 30:25)
• In Esther’s time “many of the people of the land became Jews” (Esther 8:17, 9:27)
• Even in NT times, many Jewish synagogues were attended by godly gentiles converted to Judaism (Acts 13:16, 26, 16:14, 17:17)
• Many Jewish proselytes came to worship in Jerusalem (John 20:20, Acts 2:9-11)
• Jesus quotes Isa 56:7, “My house shall be a house of prayer for all nations”, Mark 11:17.
• Further, biological Israelites could opt out of the covenant and be cut-off (Ex 30:33, 38, 31:14, Lev 7:20, 21, 25, 27).

Thus, it is abundantly clear that membership of Israel was always open to all and voluntary. See also “Pagan Salvation” for the logical extension of this idea. The distinction between a biological Jew/Israelite and a convert becomes extremely blurred if meaningful at all.

Paul confirmed this when he write:

Rom 9:6 - For not all who are descended from Israel are Israel.