Galatians 3:16-17 Now the promises were made to Abraham and to his offspring; it does not say, "And to offsprings," as of many; but it says, "And to your offspring," that is, to one person, who is Christ. My point is this: the law, which came four hundred thirty years later, does not annul a covenant previously ratified by God, so as to nullify the promise. (NRS)
This verse seems to say that Mount Sinai came 430 years from the day the promise was made to Abraham. But that cannot be.
Exodus 12:41 And it came to pass at the end of the four hundred and thirty years-- on that very same day-- it came to pass that all the armies of the LORD went out from the land of Egypt. (NKJ)
It looks like the Children of Israel left Egypt on the anniversary of the day that Jacob entered Egypt with all his family.
I had been taught that it was the anniversary of the day the promise was made to Abraham. Hmmmm. I'm learning myself here. Wonder where my teachers got the idea that it was also the anniversary of the Covenant of promise to Abraham. Need more research. Maybe the 430 years was from the day the Covenant of promise was "ratified by God" . And God "ratified" His promise with a sign - that of saving Jacob and family in Egypt, through Joseph.
Reminds me that God made a promise to Adam/Eve that He would crush Satan's head. He ratified that Covenant (4000 years later) by the death and resurrection of Christ -- this "sign" so that human beings could know that the promise WILL be completely fulfilled.