The great Old Testament patriarch Abraham is known as the father of many nations. This is what his name literally means. But Abraham did not start out that way. He started out as Abram, which means exalted father. He lived in the land of Ur of the Chaldeans. There was nothing special about him.
But God made him the Father of many nations. Abram left home to follow God’s call to the land that God would someday give to Abram’s descendants, the Promised Land of Israel. This began 100 years of living in tents for Abram.
Through it all Abram trusted God. When he promised to make his descendants as numerous as the stars of the sky, even though Abram and his wife, Sarah, had no children in their old age, Abram believed God. When God instituted the covenant of circumcision, Abram did not hesitate but circumcised all the males in his family.
And when God gave Abraham the ultimate test, asking him to sacrifice his son Isaac, he didn’t hesitate but prepared to sacrifice his son. For these and many other acts of faith, God enabled Abraham to become the father of many nations.
As Paul explains in Romans 4, Abraham is the father of all those who believe in God’s blessed promises:
That is why [everything] depends on faith, in order that the promise may rest on grace and be guaranteed to all [Abraham’s] offspring – not only to the adherents of the law (the Jews) but also to those who share the faith of Abraham, he is the father of us all.” (Romans 4:16)
People become the children of Abraham not by being physically descended from Abraham but by having the same faith as Abraham. He is the father of all who believe God’s promise that in his offspring, namely in Jesus, all nations of the earth shall be blessed.
In a sense we could also say that God did not start out as the Father of many nations. It’s true he is the source of everything, the creator, the only true God.
But throughout the Old Testament, to be honest, he is pretty much just the father of the Israelites. The rest of the peoples of the world were left to fend for themselves. But when Jesus came all that changed. In a sense, Jesus made God the Father the Father of all nations.
Paul says in 2 Cor. 5:15, Christ died for all people. In Romans 8 Paul writes that God “did not spare his own Son, but gave him up for us all.”
After Jesus died for us on the cross, rose from the dead and ascended into heaven, he poured out the Holy Spirit on his followers on the Day of Pentecost. On that day the Good News was proclaimed to people from all over the entire world:
And they were amazed and astonished, saying, “Are not all these who are speaking Galileans?  And how is it that we hear, each of us in his own native language?  Parthians and Medes and Elamites and residents of Mesopotamia, Judea and Cappadocia, Pontus and Asia,  Phrygia and Pamphylia, Egypt and the parts of Libya belonging to Cyrene, and visitors from Rome,  both Jews and proselytes, Cretans and Arabians—we hear them telling in our own tongues the mighty works of God.” (Acts 2:7-11)
So in a sense, God did not become the father of many nations until the Good News of God’s salvation in Christ was proclaimed to all people on the Day of Pentecost.
It was a tremendous challenge for the early church to welcome these non-Jews into the faith.
And since our heavenly Father did not spare his own Son but gave him up for us all he will graciously give us all things. He will support us when we are tempted. He will help us fight against the snares of the devil, the world and our sinful nature. He will keep us in the true faith until we die.
In James 1:17–18 James says:
Every good gift and every perfect gift is from above, coming down from the Father of lights, with whom there is no variation or shadow due to change.  Of his own will he brought us forth by the word of truth, that we should be a kind of firstfruits of his creatures.
Sometimes Christians get the idea that we are now God’s chosen ones, that he is not the father of many nations, just the father of us. That is certainly what the people of Israel believed in the Old Testament.
But we can’t keep God to ourselves. He is the father of all nations. We want to keep God for ourselves when, in fact, through Christ he is and always will be the father of all nations.
Jesus said in Matthew 28:19–20 “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.”
Abraham did not start out as the father of many nations but by God’s grace he became the father of many nations, the father of all who believe God’s promises. It was not until Jesus came and died for all people, rose from the dead and poured out his Holy Spirit that God truly became the father of all nations. We can’t keep this Good News just to ourselves. It belongs to everyone.