In English, we capitalize proper nouns to distinguish them from other nouns, but the biblical Greek language made no such distinction. In English, some words remain the same in meaning whether or not they are capitalized. For example, “dog” and “Dog.” But what about “mark” and “Mark”? In that grammatical differentiation, graffiti becomes a person.
In the Bible, there is a huge difference between God, the Holy Spirit, the Giver, and the holy spirit, which is the gift of His divine nature. “The Holy Spirit” is simply another name for the Only True God, the Father of Jesus Christ. Through Christ, it is He who gives the gift of his divine nature, holy spirit, to each person who makes Jesus Lord. God is spirit (John 4:24), and holiness (Isa. 6:3) is His chief characteristic, so it makes sense that He is often referred to as “the Holy Spirit.”
It is the context of Scripture, both immediate and overall, that determines whether the words “holy spirit” refer to the Giver or the gift, and whether they should be capitalized. We recommend the following book and booklets for a deeper look at this topic: “The Gift of Holy Spirit: The Power To Be Like Christ;” “34 Reasons Why the Holy Spirit is not a Separate ‘Person’ from the only True God, The Father;” “47 Reasons Why our Heavenly Father has no Equals or ‘Co- Equals;’” and “What Is True Baptism?” Listen to our audio teaching: “The Holy Spirit: Who? What? When? How? Why?” Also see our class: “One Day With The Creator,” Segment 18. We also have an article: “What Is Speaking In Tongues and Why Does God Say To Do It?”