And then there is this little nugget;
Job 2
9Then his wife said to him, “Do you still hold fast to your integrity? Curse God and die!”
To say the entire bible contains the One True Gospel, is not to say any verse isolated from the whole teaches the full gospel message. Not even I Corinthians 15:1-4 teaches the full gospel message, even though it is the One True Gospel.
However, if the above verse from Job Chapter 2 is studied in its context, exegesis will reveal a message of the One True Gospel of grace in this passage.
When are we going to get this answer? What good news did Judas preach? How many times does Saint John W have to ask before it is answered?
Sorry, but I have John W on ignore and do not see all his posts, anymore. Plus, most of his remarks are not to be taken very seriously, IMO. However, to answer your question, I would define the One True Gospel as being taught in 5 major ways:
1. Grace being an eternal attribute of God, is revealed to undeserving sinners, to the saving of their souls, from sin, death, and the powers of the devil.
2. Grace comes in covenant (promise) form, to all who were decreed to be redeemed in Christ before the foundation of the world.
3. Grace is irresistible. God's promises do not change and cannot be thwarted by the negative or neglect of will or sinfulness of men.
4. Grace that was promised, fulfilled, and manifested in the Incarnate Christ Jesus, and His righteous works, death, resurrection, and ascension alone.
5. Grace that comes to the redeemed by the unconditional gift of faith to believe the One True Gospel of Jesus Christ, from God alone.
All five of these definitions (plus many others) of God's grace are found throughout the writings of the entire bible.
These are all revealed through Covenants from God, the primary being the Covenant of Works and the New Covenant of Grace, which issue forth from the Everlasting Covenant of Redemption established within the Godhead, before the creation of the world. Ephesians 1:3-4
Gospel and Covenant are synonymous.
The first time the One True Gospel of Jesus Christ was proclaimed, was by God covenanting to produce a Seed to remedy the fall of mankind in the garden, by the deception of the devil. God promised Eve a Seed from her would crush the head of the serpent who deceived her. Genesis 3:15
This Covenant and act of remedial/saving and divine grace was fulfilled in the Seed of Eve; the Seed of David; conceived in the womb and born of woman, under the Law, in the fulllness of time, in the birth of Jesus Christ, His life, His sacrificial death, and His resurrection. Hebrews 2:9-18
This is only a very brief answer to the most important subject man can study . . The One True Gospel of Jesus Christ, as promised and taught throughout the Holy Word of God.