The Holy Spirit’s Witness of Truth:

In order to answer the question “How does the Host Spirit witness Heavenly Father’s Truth?” one must start with the role and mission of the Holy Spirit.  This is because the Holy Spirit is the spirit of truth:

John 16:13 –  Howbeit when he, the Spirit of truth, is come, he will guide you into all truth: for he shall not speak of himself; but whatsoever he shall hear, that shall he speak: and he will shew you things to come.

One thing we know about the Holy Spirit’s mission is that he is the author of scripture.

2 Peter 1:20-21 –  Knowing this first, that no prophecy of the scripture is of any private interpretation.  For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost.

This means scripture is the witness of the Holy Spirit.  We can know that this is a very powerful witness because the Holy Ghost brings us to faith using the scripture he inspired.

Romans 10:17 – So then faith cometh by hearing, and hearing by the word of God.

We can also know that this witness is still valid today because it “liveth and abideth for ever”.

1 Peter 1:23 – Being born again, not of corruptible seed, but of incorruptible, by the word of God, which liveth and abideth for ever.

In fact James calls the Holy Spirit’s witness, God’s Word, the word of truth.

James 1:18 – Of his own will begat he us with the word of truth, that we should be a kind of firstfruits of his creatures.

It is agreed that the Holy Spirit reveals the truth to us.  He does so by his witness.  His witness is the scripture he inspired.