Ok, like the title says; let's have a show of hands! Do you believe our Lord is always honest with us? How would you know? Well, I hope your answer is yes on the first question, and "because the Bible tells me" on the second one.
In Matthew, God says, "Heaven and earth will pass away, but my words will never pass away, (Matt 24:35). Now, that's the inalienable truth! When God tells us something, we can count on it. Let me remind you of something you already know, and that is; how do we know God's word will last forever? (Please note that when the word "word" it is what God is speaking, while when we see the word "Word", it is speaking of Jesus, who is the eternal Word).
But going back; again, how do we know the word is eternal? Answer; because all things God says are true, and the purest truth is everlasting because it is pure and holy, meaning it is absent of the corrosion of sin.
Just one more thing, class, and you will be dismissed. In this age of enlightenment, theologians have a better understanding of the word of God, the Bible. Of course, there will always be some who pervert the meaning of the word of God, but I'm speaking of those seeking the truth in the Spirit of the Lord. Even today, many still trust what "grandpa" said over what the Bible says about some of our founding principles. But though grandpa may have been seeking the facts of the matter, his understanding may have been off a bit.
In short, no matter what anyone tells you about what the Bible says; it's us to you to search the Scripture for the exact meaning of what you are reading or being told. God wants you to know the Truth, (Jesus), and He wants you to know His word will enough to "Do your best to present yourself to God as one approved, a worker who does not need to be ashamed and who correctly handles the word of truth," (2 Timothy 2:15). Traditions aren't always accurate. Read for yourself to understand and test what you believe. Blessings!