Throughout this work I will use the titles Gospel and New Testament interchangeably to refer to the 27 books that comprise the canon of scripture that was finished a little less than 2,000 years ago. Using the Gospel, I will show that it approves its own validity as God's word.
Certainly we cannot simply conclude that the Gospel is true just because it claims to be true. If that were so, then any number of ancient texts from various cultures would have an equally valid claim. However, we can infer something from the fact that the Gospel asserts its own validity: namely that it cannot be half-true. If the Gospel is something only near to the truth, then its assertion to be errorless and thus God's word should make us believe that it truly is errorless. By contrast, if it were not near to the truth, it would be made even farther from the truth by its own assertion of divine authorship while containing untruths.
“Heaven and earth will pass away, but my words will not pass away.” (Mt. 24:35)
“Heaven and earth will pass away, but my words will not pass away.” (Mrk. 13:31)
“Heaven and earth will pass away, but my words will by no means pass away.” (Luk. 21:33)
“But the Counselor, the Holy Spirit, whom the Father will send in my name, he will teach you all things, and will remind you of all that I said to you.” (Jn. 14:26)
As they were reminded by the Holy Spirit, the authors of the Gospels described the words of Jesus exactly and without errors.
“I tell the truth in Christ. I am not lying, my conscience testifying with me in the Holy Spirit.” (Rom. 9:1)
Peter equates Paul's letters with former (Old Testament) scriptures: (2Pet. 3:16) “as also in all of his letters, speaking in them of these things. In those are some things hard to be understood, which the ignorant and unsettled twist, as they also do to the other Scriptures, to their own destruction.”
Thus you are faced with a stark choice: Believe the Gospel accounts in their entirety or reject them as nothing more than an historical myth.
Gospel about validity of Old Testament
If one truly believes what is recorded in the Gospel, this belief also necessitates a belief in the accounts recorded in the Old Testament. The reason being, oftentimes the New Testament refers to the Old Testament as a proof text for many of its claims. Here are some examples:
“For most assuredly, I tell you, until heaven and earth pass away, not even one smallest letter or one tiny pen stroke shall in any way pass away from the law, until all things are accomplished.” (Mt. 5:18)
“But it is easier for heaven and earth to pass away, than for one tiny stroke of a pen in the law to fall.” (Luk. 16:17)
“The book of the generation of Jesus Christ, the son of David, the son of Abraham. …” (Mt. 1)
“… for thus it is written through the prophet…” (Mt. 2:5)
“that it might be fulfilled which was spoken by the Lord through the prophet.” (Mt. 12:15)
“He said to them, ‘This is what I told you, while I was still with you, that all things which are written in the law of Moses, the prophets, and the psalms, concerning me must be fulfilled.’” (Luk. 24:44)