Once internationalism was outlawed in Tower of Babel incident in Genesis 11 and with the inauguration of nationalism, we have a scattering of nations geographically, linguistically, and racially. This demands missionary activity. Abraham was the first foreign missionary. He was born a Gentile and became a Jew by faith belief in the future Messiah, Jesus Christ. Gen. 15:6.
“Therefore its name was called Babel, because there the LORD confused the language of the whole earth; and from there the LORD scattered them abroad over the face of the whole earth.” (Genesis 11:9, NASB)
“Then he believed in the LORD; and He reckoned it to him as righteousness.” (Genesis 15:6, NASB)
The first title for a missionary was “Hebrew,” which means “one who crosses over the river.” Abraham became a Hebrew. He crossed over the River Euphrates and came into Canaan and evangelized. Converts were Aner, Mamre, Eshcol and many others. Gen. 14:13.
“Then a fugitive came and told Abram the Hebrew. Now he was living by the oaks of Mamre the Amorite, brother of Eshcol and brother of Aner, and these were allies with Abram.” (Genesis 14:13, NASB)
In the Age of Israel, Jews were responsible for custodianship of the Word and dissemination of the Gospel. Rom. 3:2.
“Great in every respect. First of all, that they were entrusted with the oracles of God.” (Romans 3:2, NASB)
Israel was a missionary base because they had custodianship of the Word. Those who became born-again were to grow in grace and knowledge of the Savior and to evangelize. Jews were to go to the Gentiles and bring them the message of the Gospel. An example was Jonah.
The first failure was when Jews generally failed to accept the Messiah to come, Jesus Christ as Savior. Instead, they accepted the Mosaic Law as a way of salvation and sought human righteousness as the basis of salvation rather than divine righteousness, which can only be credited to the individual on the basis of faith in Jesus Christ.
The second failure was having failed at the point of salvation, they failed at the point of missions. You cannot become a missionary unless you are born-again. Their failure led to a change in dispensation and in administrators and the fifth cycle of discipline for Israel. During their fifth cycle of discipline, the Church is the missionary base.
Even though Israel failed, God used other means and Gentiles were saved in Old Testament times. Rom. 9:30-33.
“What shall we say then? That Gentiles, who did not pursue righteousness, attained righteousness, even the righteousness which is by faith; but Israel, pursuing a law of righteousness, did not arrive at that law. Why? Because they did not pursue it by faith, but as though it were by works. They stumbled over the stumbling stone, just as it is written, "BEHOLD, I LAY IN ZION A STONE OF STUMBLING AND A ROCK OF OFFENSE, AND HE WHO BELIEVES IN HIM WILL NOT BE DISAPPOINTED."” (Romans 9:30-33, NASB)
In fact, probably more Gentiles were saved in the Old Testament than Jews according to this passage. Jews had a perfect system for disseminating the Gospel: Levitical feasts, offerings, Holy Days, etc. They will again evangelize during the Tribulation. This is part of their future.