The Lord Jesus Himself said (speaking of Moses) "If ye believe not his writings, how shall ye believe My words?" John 5:47. His words were the words of God; He does not contrast the authority of what He said with that of the written Word, but with the means of communication. God has been pleased to employ that means as a permanent authority. Peter says, "No prophecy of the Scripture..." (2 Pet. 1:20). There have been many prophecies which are not written; they had the authority of God for those persons to whom they were addressed. For the Word speaks more than once of prophets -who must therefore have prophesied-without communicating their prophecies to us.
A multitude of things spoken by Jesus Himself are not reproduced in the Scriptures (John 21:25); so that it is not only a question of from whom we have heard a truth, but also of the character of that which has been communicated. When it is for the permanent profit of the people, or of the assembly of God, God caused it to be written in the Scriptures, and it abides for the instruction and the food of His children in all ages....
The Scriptures are the permanent expression of the mind and will of God furnished as such with His authority. They are the expression of His thoughts. They edify, they are profitable, but this is not all-they are inspired....
They teach, they judge the heart, they correct, they discipline according to righteousness, in order that the man of God may be perfect; that is, thoroughly instructed in the will of God, his mind formed after that will and completely furnished for every good work. The power for performing these comes from the actings of the Spirit. Safeguard from error, wisdom unto salvation, flow from the Scriptures; they are capable of supplying them....
Does this perfect and supreme authority of the Scriptures set aside ministry? By no means; it is the foundation of the ministry of the Word. One is a minister of the Word; one proclaims the Word- resting on the written Word which is the authority for all, and the warrant for all that a minister says, and imparting to his words the authority of God over the conscience of those whom he teaches or exhorts.... That which the Word says silences all opposition in the heart or mind of the believer. It was thus that the Lord answered Satan, and Satan himself was reduced to silence (Luke 4:1.13). He who does not submit to the words of God thereby shows himself to be a rebel against God.... The Old Testament left untold the history of Christ, the mission of the Holy Ghost, the formation of the assembly, because these facts being not yet accomplished could not be the subject of its historical and doctrinal instructions, and the assembly was not even the subject of prophecy. But all is now complete, as Paul tells us that he was a minister of the assembly to complete the Word of God (Col. 1:25). The subjects of revelation were then completed. God's Word speaks of grace as well as truth. It speaks of God's grace and love, who gave His only begotten Son that sinners like you and me might be with Him, know Him-deeply, intimately, truly know Him-and enjoy Him forever, and enjoy Him now, that the conscience perfectly purged might be in joy in His presence, without a cloud, without a reproach, without a fear. And to be these in His love, in such a way, is perfect joy. The written Word will tell you the truth concerning yourself; but it will tell you the truth of a God of love, while unfolding the wisdom of His counsels....
Let me add, to my reader, that by far the best means of assuring himself of the truth and authority of the Word, is to read the Word itself.