Generally speaking, the Bible is regarded by Christians as the primary source of the truth of God.
And not withstanding that there are translation errors, versions, as well as being subject to private interpretations. Thus, denominations.
The Bible is the written Word of the Author, the Holy Spirit, who is the primary source of truth. That is why He was sent as our Teacher. So to seek the truth we need to sit at His feet, so to speak, through being baptized in Him by Jesus.