The Holy Spirit will convince other Christians through what is revealed in the Bible whether one is presenting the truth or not. We are not left to our own devices, but the Holy Spirit is the Divine Teacher of every child of God.
Let's take the Bible truth that Jesus is God. Is that plainly stated in Scripture? Absolutely. So how do we know this? From many passages, but one of the clearest is Hebrews 1:8,9: But unto the Son he saith, Thy throne, O God, is for ever and ever: a sceptre of righteousness is the sceptre of thy kingdom. Thou hast loved righteousness, and hated iniquity; therefore God, even thy God, hath anointed thee with the oil of gladness above thy fellows.
1. Who is addressing the Son of God? God the Father
2. Does the Father call the Son "God"? Absolutely
3. Does the Father confirm the eternal throne of the Son? Absolutely
4. And yet is God the Father the God and Father of Jesus Christ? Absolutely
5. Who are the "fellows" of Christ? They are the partners or partakers or sharers with Christ, and that means all the children of God.
6. Can these things be comprehended with the natural mind? No
7. Will all genuine children of God agree that Jesus is God? Absolutely.