Spoken by the Lord
How shall we escape if we neglect so great a salvation, which at the first began to be spoken by the Lord, and was confirmed to us by those who heard Him. (Hebrews 2:3, emphasis added)
Most scholars believe the concept of salvation is first spoken in Genesis 15:6 in reference to Abraham, the father of faith, “And he believed in the LORD, and He accounted to him for righteousness.” Thus the logical assumption is made of Hebrews 2:3 that the words spoken of by the Lord Jesus included those of the Old Testament (where the message of salvation begins to be threaded through the entire Bible, from cover to cover), not just the New Testament in which the words of His fleshly visitation are recorded.
Kenneth Wuest in Hebrews in the Greek New Testament treats this Hebrews 2:3 passage, within the context of Hebrews, as endorsing the whole of New Testament Scripture as the words of Christ for in total the New Testament is the announcement of salvation:
“But the message of salvation given by the Lord was in its character, final. He was not only the Spokesman but the One who brought into being and made available to believing sinners, the salvation which He announced. Our Lord announced the New Testament as taking the place of the First Testament, when He said, ‘This is my blood of the New Testament, which is shed for many for the remission of sins.’ (Matthew 26:28)”
This passage also affirms the New Testament as truth and the words of Christ because it was confirmed by those who were eyewitnesses to His message and the presentation of the reality of New Testament, by the apostles themselves.
With all this said it can only be concluded that we can count the totality of Scripture as Christ’s words and are to be included in our call of “teaching them to observe all things that I have commanded you.” (Matthew 28:20a)