2 Peter 1:2
Adherents of the Trinity doctrine assert that the Holy Spirit is a personality alongside the Father and the Son. Yet, when the apostles—especially Paul—referred to the God Family in their epistles, why is mention of the Holy Spirit almost totally absent (James 1:1; II Peter 1:2; I John 1:3; Romans 1:7; I Corinthians 1:3; II Corinthians 1:2; Galatians 1:3; Ephesians 1:2; Philippians 1:2; Colossians 1:2; I Thessalonians 1:1; II Thessalonians 1:2; I Timothy 1:1-2; II Timothy 1:2; Titus 1:4; Philemon 1:3)?
Where is the Holy Spirit? Is James not a servant of the Holy Spirit (James 1:1)? Is he a servant only of God and of Jesus Christ? What about "knowledge of the Holy Spirit" in II Peter 1:2? Is there no "fellowship with the Holy Spirit" in I John 1:3? Why do the apostles ignore it?
They include a greeting from the Father and the Son in each of these letters, but there is no greeting from the Holy Spirit. This was inspired by God! Is it possible that this is evidence that there is no other personality? Little by little, it keeps adding up. We need to see this with our own eyes—the Holy Spirit is ignored every time the God Family is mentioned. Father and Son—yes. Holy Spirit—no.
With a few variations in words, every apostle ignores the Holy Spirit. Would it not be gross insubordination for them to recognize two in the highest offices in the universe and totally ignore the third? They did this because they did not know the Holy Spirit as a personality within the God Family because Jesus taught them no such thing. The Holy Spirit is the power God uses to direct and carry out His purposes within His creation.
John W. Ritenbaugh
The Holy Spirit

Growing in the knowledge of God and of Jesus Christ involves real conversion—the transformation of our characters, intellects, emotions, actions, words, and thoughts from the evil way inspired by Satan and man's carnal nature into the divine nature of God Himself. Because the Father and Christ have given us so much, we must add virtue, knowledge, self-control, perseverance, godliness, brotherly kindness, and love to our faith. Notably, when the apostles greeted the churches, they mentioned knowledge of and fellowship with the Father and the Son, but ignored the Holy Spirit every time the God Family is mentioned. They did this because Jesus taught them no such thing—the Holy Spirit is the power God uses to direct and carry out His purposes, not a personality.