As a preacher of the Gospel and teacher of the Bible the subject of this exposition is on the "Holy Scriptures". Paul, Luke, and John lived during the days of Christ. During the years of Christ and His death and resurrection a great transition was made between the Old and New Covenants. The Holy Scriptures at that time were Old Testament records and were used as a basis for Israel's faith. During the first century the Four Gospel's and the New Testament Epistles were being written and were not published until the 3rd century and after. The Old Testament records (the Holy Scriptures) were Israel's primary written words of God.
In the verses used below the Holy Scriptures mentioned were referring to Old Testament records about Christ. These New Testament Spirit led writers and holy men of God were writing and testifying to power of a resurrected and exalted Christ they had witnessed and experienced in their hearts and lives. The Old Testament records they wrote about would consist of the Law of Moses, the Prophets, and the Psalms. These sacred oracles were given to Israel as a basis of their faith toward God. These Holy Scriptures contained prophecies, promises, and the commandments which were the greatest set of morals ever written. The Holy Scriptures were sacred Jewish writings and contained concealed revelations of the Messiahship of Christ. The Torah (the first five books of the Old Testament) contained all of the blessed moral standards Israel were to live by. These God-given morals kept Israel holy and in right-standing enough to point the Jew to their future hope of the Anointed One, the Promised Messiah.
Many concealed prophecies were brought to light in the actual birth, life, ministry, death, burial, and resurrection of Israel's Promised Messiah. His name was Jesus. He was the righteousness of God in the flesh. He was foretold by the Prophets and actually proven by the truth contained within the Holy Scriptures. The Holy Scriptures were able to reveal and confirm the truth about the promised Christ. The Holy Scriptures contained within the Old Testament records were used as a basis for faith during the life and ministry of the writers of the New Testament records. Luke, John, and Paul used and confirmed the truth about Christ that was found within Old Testament records during the first century.
Here are a few examples of how the Apostle Paul defined the true Gospel and how other holy men of God defined the Holy Scriptures. All records below from the Gospels and the New Testament Epistles pointed to Old Testament records the Spirit filled writers termed as the Holy Scriptures.
Paul instructed Timothy to use Old Testament records as a basis for faith in Christ.
2 Tim. 3:16-17...And that from a child thou hast known the holy scriptures, which are able to make thee wise unto salvation through faith which is in Christ Jesus. All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: That the man of God may be perfect, thoroughly furnished unto all good works.
Moses' writings were the 613 commandments contained in the first (5) books of the Old Testament.
John 5:39-47...Search the scriptures; for in them ye think ye have eternal life: and they are they which testify of me. And ye will not come to me, that ye might have life. I receive not honour from men. But I know you, that ye have not the love of God in you. I am come in my Father's name, and ye receive me not: if another shall come in his own name, him ye will receive. How can ye believe, which receive honour one of another, and seek not the honour that cometh from God only? Do not think that I will accuse you to the Father: there is one that accuseth you, even Moses, in whom ye trust. For had ye believed Moses, ye would have believed me: for he wrote of me. But if ye believe not his writings, how shall ye believe my words?
Jesus preached this first Gospel sermon.
Luke 24:44-46...And he said unto them, These are the words which I spake unto you, while I was yet with you, that all things must be fulfilled, which were written in the law of Moses, and in the prophets, and in the psalms, concerning me. Then opened he their understanding, that they might understand the scriptures, And said unto them, Thus it is written, and thus it behoved Christ to suffer, and to rise from the dead the third day:
This is how Paul defined the Gospel.
1 Cor. 15:1-4...Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand; By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain. For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures; And that he was buried, and that he rose again the third day according to the scriptures: