Below is an email sent to some students summarizing a set of classes in Romans 3 which I recently concluded.  Since the email was originally only meant to summarize the contents of the classes for those who attended, the language and grammar are a bit irregular, and I am not going to take the time here needed to smooth them out.  Nonetheless, I hope the summary conveys the gist of the global, timeless, and unchanging aspects of the gospel message.

We discovered that the gospel, the good news, is "God's promise of salvation to humankind to those who have faith."  We learned the staggering truth that the gospel delivered to Cain and Abel (remember our Hebrews 11 study?) was the same gospel delivered to King David, which was the same gospel delivered to John the Baptist, which was the same gospel delivered by Jesus, which was the same gospel delivered by Paul, and is the same gospel we deliver to the world today! 

Just one gospel.  God saves sinners on the basis of the faith they place in Him as Savior.  Before the Law, Abraham was saved by faith in God.  During the Law, the Law saved no one--it was not the gospel.  During the Law, people were saved only by faith; they had their hearts renewed, their spirits revitalized, and their sins forgiven on the basis of faith.  After the Law, now, people are saved only by faith, and their hearts are renewed, their spirits made alive again, and their sins forgiven. 

The only difference between then (during the Law) and now is that we know now that Christ is the begotten God, the God Who became a man, to save His creatures.  Before He came, during the Law, they knew only that God saves.  How did God save before Jesus became the sacrifice?  The animal sacrifices did not save, but God did "pass over" sins confessed with an animal sacrifice, but He only passed over them until the final sacrifice.  That final sacrifice brings forgiveness of all past sins, present sins, and all confessed future sins.  The animal sacrifices were symbols of the faith that the people had placed in God, as Savior, and God promised them He would forgive them.  God always honors His promises. 

Salvation is always a promise of ultimate final redemption.  Salvation is both "now" but "not yet."  We have the renewed hearts and spirits now, the promise of ultimate salvation now, and the Holy Spirit as the guarantee of that ultimate salvation now.  But what need do we have of a promise if we have salvation now?  Because there is a final redemption coming, a final change from this corruptible body (which will be resurrected) into an incorruptible body for eternal life with God--He has promised and God never lies.  We have salvation now, but the final form of it yet to come.

The gospel, the promise of God's salvation on the basis of faith, has not changed age to age.  The exact nature of the fulfillment of that promise, that is that Jesus is the fulfillment of the promise via His life, death, and resurrection, was not given until 2000 years ago, but the gospel itself, the promise of God's salvation on the basis of faith, is still the same as it always was.  The Law never saved anyone, faith in the Law never saved anyone, and faith in sacrifices did not save anyone.  Faith in God saved all who believed, all who believe, and all who will believe.

As Paul said, a Jew could be a Jew via his blood line, and keep the Law (as best he could), but not be a Jew in heart, and so not be a spiritual son of Abraham, but merely a son of Adam.  A gentile may ignore the Law of Moses but embrace Christ by faith and so become a spiritual son of Abraham in spite of having once been a son of Adam.  So it is our goal to be known as sons and daughters of Abraham, spiritual Jews, adopted by God our Father, joint heirs with Christ.

Scripture Passages on the continuity of the gospel message:

There only ever was one Savior of humanity

Isaiah 45:21, 49:26, John 4:42

Messiah (the coming Savior) foretold (not a contradiction of Isaiah 45:21, but the fulfillment of it)

Daniel 9:25-26, Isaiah 9:6-7, Jeremiah 31:6-13

There never was a distinction between Jews and Gentiles

Romans 3:22, Jeremiah 3:17

All humanity sinned - Jews and Gentiles

Romans 3:23, Isaiah 53:6-7, Psalm 14:1-3

One gospel for all humanity for all time

Hebrews 10:38-12:3, Matthew 4:23, 9:35, 11:5, 24:14, 26:3, Mark 1:1, 1:14, 8:35, 10:29, 13:10, 14:9, 16:15, Luke 3:18, 4:18, 7:22, 9:6, 16:16, 20:1, Acts (seamless transition from the gospel of faith and repentance that Jesus taught to the gospel of faith and repentance that Paul ended up teaching)

Old Testament View of What Happens to a Man of Faith

New Heart: Ezekiel 36:25-26, 18:30-31, Psalm 51:9-13, Jeremiah 32:40

Spirit Made Alive: Nehemiah 9:30-31, Psalm 104:29-30, 139:4-10, Isaiah 57:15, 63:10, Lamentations 5:21, Titus 3:5

Yes, the gospel was always the same, as was the means of salvation:  God saves by His mercy and grace those who have faith in Him, and He gives them a new spirit and a renewed heart--that's a promise!