What is the Abrahamic Covenant?
(1) Is it for the selection of the Seed?
Its promise is THE SEED: (1) Jesus; (2) The Christ; (3) The earthly seed through them.
(2) Or is it the blessing of all the families of the earth?
Ultimately, yes. The result will bless all the nations.
(3) When did it begin—with Abraham, Isaac or Abel?
With Jesus Christ: but its provisions extend backward and forward to all who have exercised "the faith of Abraham."
(1) Is it proper to say that the Sarah and Abrahamic Covenants are one and the same thing?
The Abrahamic Covenant primarily is the Sarah Covenant—the Faith or Promise Covenant.
(2) Under what Covenant were the Ancient Worthies developed, Abrahamic or Sarah?
The Abrahamic or Faith Covenant, typified by Sarah. All justified by faith are of this Covenant. The others are covenants of works.
(3) Are the Ancient Worthies the fleshly seed, or are the Jews who come under the New Covenant in the Millennial Age the fleshly seed?
The Ancient Worthies primarily, but all who ever come to the Faith and Works relationship under the New Covenant will, as children of "the Anointed," be grandchildren of Abraham, who typified God—the Father.
(4) Is the Sarah Covenant as comprehensive as the Abrahamic Covenant?
No! It relates only to the "Seed of Promise."
(5) Does the Sarah Covenant come to an end at the close of the Gospel Age?
(6) Does the Sarah Covenant end when the last member of the spiritual Seed is born, or does it end after the Ancient Worthies come forth?
After both: the two being shown in Joseph and Benjamin.
(7) If the Sarah Covenant brings forth the spiritual Seed, how can we say that both seeds are brought forth under the Abrahamic Covenant?
The dual feature is shown in Rachel.
(8) If both the seeds are brought forth under the Sarah Covenant then how about Gal. 3:16, where it speaks of THE Seed which is Christ?
The Christ is the Seed, but the "promise" is "sure to both."—Rom. 4:16.
(9) Are those now called to membership in The Christ justified by the sacrifice of the man Christ Jesus?
Most assuredly, "By faith in his blood." Faith in the New Covenant justifies nobody. Those blessed under the New Covenant will be justified by works.—Rev. 20:13.