Believers in Jesus have to take everything on trust about him. No historical eyewitness saw Jesus and no one wrote down verbatim what he said. His name does not even appear in any text until the end of the second century in fact neither does his description "Christ" appear until much later. The Greek text says Chrestus meaning "good" [man], the same word was used to designate earlier God-men saviours. In the early centuries he was mainly known just as "the Lord".
As for the "Word of God" this was borrowed, like much NT material from current Greek philosophy giving some needed gravitas to the Christian text.
I suggest that the reason the text at Heb 13;8 was included in the BIble was because the concept of Jesus as the Son of God and the Chrestus was constantly changing and the bishops (yes they had bishops: episcopoi) needed to stamp out dissent and give some clarification. Note the context; Heb 13:9 warns "not to be led astray by all sorts of strange doctrines". JB
Like the JW doctrines today, beliefs about Christ (and everything else) change over time, JWs no longer worship Jesus for example, and are based on expediency, that is, what is now favourable to believe for the sake of the furtherance of the cult.