Now the Promises were made to Abraham and to his offspring; it is not said, 'and to your offsprings' in the plural, but in the singular and to your offspring — which is Christ.
The promise made to Abraham and his offspring that he should inherit the world, did not reach him through the Law, but through the righteousness of faith.
That is why all turns upon faith; it is to make the promise a matter of favour, to make it secure for all the offspring, not simply for those who are adherents of the Law but also for those who share the faith of Abraham — of Abraham who is the father of us all
Besides, Scripture anticipated God's justification of the Gentiles by faith when it announced the gospel beforehand to Abraham in these terms: All nations shall be blessed in thee.
Now you are the sons of the prophets and of the covenant which God made with your fathers when he said to Abraham, all families on earth shall be blessed in your offspring.
Then what about the Law? Well, it was interpolated for the purpose of producing transgressions till such time as the Offspring arrived to whom the Promise was made; also, it was transmitted by means of angels through the agency of an intermediary