In John 18:9 we read, “This was to fulfill the word that He [Jesus] had spoken…” and in John 18:32 it gives another instance where, “This was to fulfill the word that Jesus had spoken…”
Thus, John twice tells us that Jesus’ words were to be fulfilled.
The significance of this is that John believed Jesus’ words NEEDED to be fulfilled. His words weren’t just ideas, but had divine authority, according to John, and thereby had to “come through” and be “fulfilled”.
This can further be seen when you consider that John (and other N.T. writers) see only one thing that contains words that need to be “fulfilled”: THE SCRIPTURES. For instance:
“That the word spoken by the prophet Isaiah might be fulfilled” (Jn 12:38)
“The Scripture will be fulfilled…” (Jn. 13:18)
“The word that is written in their Law must be fulfilled…” (Jn. 15:25)
“All this has taken place that the Scriptures of the prophets might be fulfilled…” (Mt. 26:56)
“the Scripture had to be fulfilled…” (Acts 1:16)
Thus, when John says that Jesus’ words need to be fulfilled (18:9, 32), he clearly believes Jesus’ words have the same authority and power of Scripture (which was only the Old Testament books at the time of Jesus’ ministry).
And thus, from words penned by one of Jesus’ first followers, Jesus carried an authority that was greater than any man. His words were divine and believed to be divine from the beginning. This is the God we serve, whose words are as eternal as His nature.