Would you not?
continuation of answer...
What reference point is used by all Christians? The Bible. God's Word. Interpret that as you will, but if the Bible, which we I presume would agree, contains God's Word then it would contain the truth since God, unlike us, cannot lie.
I sense your argument already of Matthew 16:18 and what then is the truth? Clearly you and I will disagree on that topic, but the fact of the matter is that the truth of the Gospel is hammered home to each of us in the message of salvation thru faith in Christ. That message literally explodes off the pages of the NT and if that is not the truth, then I do not know what is.
Respectfully...