Trinity Sunday, which falls on the third Sunday of June this year, ascribes to the Triune God: Father, Son and Holy Spirit.
God is the first person of the Triune God. The Son is the second person and the Holy Ghost (Spirit) is the third person. The Holy Spirit is one of God's forms, or persons. The Holy Spirit is not, of itself, a separate god, but is God Himself.
The Athanasian Creed states: "So the Father is God, the Son is God and the Holy Ghost is God. And yet there are not three Gods, but one God.
(God's actions are manifested through the three persons of God: the Father, the Son and the Holy Ghost). The same creed makes the following observation about the Holy Ghost and the Trinity of God. "The Holy Ghost is of the Father and the Son, neither made nor created nor begotten but proceeding. So there is one Father, not three Fathers, one Son, not three Sons, one Holy Ghost, not three Holy Ghosts."
The power and guidance of God's spirit is mentioned already in the Old Testament. According to the story of creation, "The spirit of God moved upon the face of the waters." (Gen 1:2). Isaiah spoke of those who rebelled and "vexed his holy spirit." Under God's wrath they remembered Moses and asked, "Where is he that brought them up out of the sea with the shepherd of his flock? Where is he that put his holy spirit within him?" (Isaiah 63:10,11). The prophets also foretold the pouring of the spirit in the last times (Isaiah 44:3). Jesus spoke of the promise of the Holy Spirit before his death, "But the Comforter, which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you." (John 14:26). The Holy Spirit is the key to understanding God's revelation. "No prophecy of the scripture is of any private interpretation" (2 Peter 1:20-21).
The Bible also speaks of God's Kingdom. The Holy Spirit dwells in His Kingdom and reveals the mysteries of faith to God's children. When Jesus began his public ministry, He said, "Repent for the kingdom of heaven is at hand." (Matthew 4:17) Also, when He taught the disciples how to pray, he said, "Thy kingdom come." (Matthew 6:10) One of the most clear-cut messages of the Kingdom was in Jesus sermon on the mount, when he said, "Seek ye first the kingdom of God, and His righteousness." (Matthew 6:33). Through His Word we understand that God has His Kingdom here upon this earth and one must find this Kingdom. Jesus said, "The kingdom of heaven is like unto treasure hid in a field, he which when a man hath found, he hideth, and for you joy thereof goeth and selleth all that he hath, and buyeth that field." (Matthew 13:44)
Luther further clarifies the existence of God's kingdom on earth, "I believe that there is on earth a holy flock and congregation of pure saints under one Head, Christ, called together by the Holy Spirit in one faith, one mind and understanding, with manifold gifts, yet one in love, without sect and schisms." John, on the Isle of Patmos was inspired by the Holy Spirit to write: "And I heard a great voice out of heaven saying, Behold, the tabernacle of God is with men, and he will dwell with them, and they shall be his people, and God himself shall be with them, and be their God." (Revelations 21:3)
The Bible states, "Not everyone that saith unto me, Lord, Lord, shall enter into the kingdom of heaven, but he that doeth the will of my Father which is in heaven." (Matthew 7:21) The Holy Spirit opens God's Word, to understand living faith. The Bible is a closed book to those who do not have the Holy Spirit. In Luther's explanation of the Third Article of the Creed, he states, "I believe that I cannot of my own reason or strength believe in Jesus Christ, my Lord, or come to Him, but the Holy spirit has called me through the Gospel, enlightened me by His gifts and sanctified and preserved me in the true faith, even as he calls, gathered, enlightens and sanctifies the whole Christian Church on earth and preserves it in union with Jesus Christ in the true faith."
Jesus told Nathanael, "Follow me" and "Come see." (John 1: 43, 46) Therefore, "Ask, and it shall be given you; seek, and ye shall find; knock, and it shall be opened unto you." (Matthew 7:7) From God's Kingdom one can hear the core message of the gospel, which is "the power of God unto Salvation to everyone that believeth." Romans 1:16, where the forgiveness of sins is preached through the power of the Holy Spirit. The Apostle Paul said, "For Christ sent me not to baptize, but to preach the gospel." (I Corinthians 1:17) John wrote: "I write unto you little children, because your sins are forgiven for His name's sake." (I John 2:12)