The Apostle Paul had just chastized the Galatians for perverting the Gospel. It is unreal that he was now telling the Galatians that a different Gospel was preached to Abraham. There is only one Gospel for all time and Paul says it was preached to Abraham.
There was another time in which this question was raised and I gave my opinion that there is indeed only one "everlasting Gospel" which is the end product or culmination of a progressive revelation having many aspects and phases with "mysteries" to be revealed at the end of the age(s) to all the inhabitants of the world.
Revelation 14:13
6 And I saw another angel fly in the midst of heaven, having
the everlasting gospel to preach unto them that dwell on the earth, and to
every nation, and kindred, and tongue, and people,
7 Saying with a loud voice, Fear God, and give glory to him; for the hour of his judgment is come: and worship him that made heaven, and earth, and the sea, and the fountains of waters.
The Gospel of the redemption of mankind which started with the promised Seed of the Woman and culminated in the death burial and resurrection of Jesus Christ for our sins.
Personally, I don't believe that the OT saints had a specific knowledge of the incarnation of Christ. Paul calls it a mystery:
1 Timothy 3
16 And without controversy great is the mystery of godliness: God was manifest in the flesh, justified in the Spirit, seen of angels, preached unto the Gentiles, believed on in the world, received up into glory.
The promise of the Messiah for the OT saints was IMO part of the everlasting gospel for which they were responsible as an integral part of their faith, but the incarnation and other of the "mysteries" yet to be revealed, they were not (although God might have revealed at least the incarnation to Abraham).
1 Peter 1
10 Of which salvation the prophets have enquired and searched diligently, who prophesied of the grace that should come unto you:
11 Searching what, or what manner of time the Spirit of Christ which was in them did signify, when it testified beforehand the sufferings of Christ, and the glory that should follow.
12 Unto whom it was revealed,
that not unto themselves, but unto us they did minister the things, which are now reported unto you by them that have preached the gospel unto you with the Holy Ghost sent down from heaven; which things the angels desire to look into.
Colossians 1
25 Whereof I am made a minister, according to the dispensation of God which is given to me for you, to fulfil the word of God;
26
Even the mystery which hath been hid from ages and from generations, but now is made manifest to his saints:
27 To whom God would make known what is the riches of the glory of this mystery among the Gentiles; which is Christ in you, the hope of glory:
So there is one gospel with many aspects, phases and "mysteries" which culminate and are "in these last days" revealed and culimated by Jesus Christ
and His Apostles
Hebrews 2
3 How shall we escape, if we neglect so great salvation; which at the first began to be spoken by the Lord, and was confirmed unto us by them that heard him;
4 God also bearing them witness, both with signs and wonders, and with divers miracles, and gifts of the Holy Ghost, according to his own will?
at the end of the age(s). That is: The redemption of mankind by the Triune God through the death burial and resurrection for sin by the God-man Jesus Christ.
Romans 16
25 Now to him that is of power to stablish you according to
my gospel, and the preaching of Jesus Christ, according to the revelation of the mystery,
which was kept secret since the world began,
26 But now is made manifest, and by the scriptures of the prophets, according to the commandment of the everlasting God, made known to all nations for the obedience of faith:
There are yet unfulfilled details connected to this "everlasting Gospel" which have to do with the Return of Christ and the Kingdom of God.
1 Corinthians 15
23 But every man in his own order: Christ the firstfruits;
afterward they that are Christ's at his coming.
24 Then cometh the end, when he shall have delivered up the kingdom to God, even the Father; when he shall have put down all rule and all authority and power.
25 For he must reign, till he hath put all enemies under his feet.
HankD
