What does this mean that “the time had fully come?” It means that Jesus is king of kings, and uses History to His own purposes.
Lest there be any doubt that He now rules as true God and true man, lest there be any doubt that He has ruled from eternity, let us see how He as king of kings molded history to his needs.
The area in the middle between the rivers is the Plain of Shinar where Noah’s descendents began to build a powerful civilization, until God scattered them by confusing their languages and dispatching them to the four corners of the world. The world was divided this way so that rather than joining in rebellion against God, the nations would be weakened so that the promise of the Savior to come would be kept alive. It would be kept alive in such a place and in such a way as to touch each of these other civilizations.
And so it continued for a long time, with city states with differing languages growing up. It was in this situation that Abraham was called, and the promise given to him that in his descendent all the nations of the earth would be blessed.
It stated that way, with all these little nations rising and falling. But then things began to change, and quickly (in historical terms). The Assyrian empire exploded, (around the name Assyria) about 640 years before Christ. Soon it was replaced by the New Babylonian, (dotted line) which took over Judea in 606 B.C.
It was at that time, 550 years before it happened, that Daniel foretold the events that followed, particularly in his vision of the great statue in Daniel chapter two.
The New Babylonian was replaced by the Median or Medo-Persian Empire (the area marked by the dot-and-dash). The Medo-Persian Empire was replaced by the Empire of Alexander the Great (long dashes) that covered nearly everything there but the boot of Italy.
Tradition has it that that when Alexander approached Jerusalem, he was met by the priests who told him he was expected, and showed him Daniel's prophecy, including the general extent of his conquests. (Alexander spared Jerusalem.)
Finally by about 100 B.C. the last of the earthly empires of Daniel had taken root and held sway over the meeting-places of three continents. This was the empire of iron, the Roman Empire, eventually extending from North Africa to Southern Russia, and from England to India.
When the time had fully come, and Jesus was born, He entered a world prepared for the gospel. One common government, one common language of commerce, freedom of commercial shipping, one system of roads, a dependable system of law enforcement, even a decent post office.
On top of that, the philosophical atmosphere created opportunities for the gospel. The nations were corrupt; faith in the old deities had been lost. It was not unusual for someone such as Paul to strike up a conversation dealing with matters religious.
So it was that as King of kings and Lord of lords, God saw to it that… when the time had fully come, God sent his Son, born of a woman, born under law, to redeem those under law.