a light for revelation to the Gentiles, and for glory to your people Israel. (ESV)
God once took a man named Abraham, and made out of him a nation unto Himself. Abraham's grand-son, Jacob, had twelve sons, out of whom came the twelve tribes of Israel. God made and chose Israel unto Himself in order to have a special relationship with Himself and this nation. Israel was God's chosen people, His elect.
God also intended Israel to be more. Israel was to be a shining example, to the peoples around them, of how one could have a proper relationship with the one true God of the universe (c.f. Isaiah 42:6). Israel was not chosen by God because of anything they did or any quality within themselves that God would see as being worthy of His choice. Through the years, the people of Israel had forgotten this fact. They became prideful, and saw people of other ethnic backgrounds as being less than themselves.
God had always intended the Gospel to for people of all ethnic backgrounds. God first indicated this in the protoevangelion (the first Gospel [c.f. Genesis 3:15]), He revealed this to Abraham (c.f. Genesis 12:2), and made it clearer through the prophecy of Isaiah (c.f. Isaiah 49:6).
In the book of the Revelation, it is recorded that Christ died to save a people out of every "ethnos" (e.i. people groups). (c.f. Rev. 5:9)
Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit,
teaching them to observe all that I have commanded you. And behold, I am with you always, to the end of the age.
As Christian, we are to share the Gospel with everyone that we come across in our daily walk no matter what their ethnic, social, or economic background is.