The Holy Spirit is the third Divine Person of the Holy Trinity. To believe in the Holy Spirit is to confess that the Holy Spirit is one of the Holy Trinity. The Holy Spirit is true God, perfectly equal to the Father and the Son, though distinct from them. Since the beginning, the Holy Spirit was already at work with the Father and the Son. If men were able to lead good and even holy lives, it was because of the guidance of the Holy Spirit. But his existence was not made manifest until the coming of Christ, who revealed to us the mystery of the three Persons in One God. The Holy Spirit first showed himself at Jesus' baptism, when he descended on Jesus in the form of a dove, while the voice of the Father echoed from heaven. He also manifested himself during the Transfiguration, as the bright cloud that covered Jesus. But his greatest manifestation was on Pentecost.
The mission of the Holy Spirit. The Holy Spirit is inseparable from the inner life of the Trinity, as well as from his gift of love for the world. In adoring the Holy Trinity, the Church also professes the distinction of persons. In their joint mission, the Son and the Holy Spirit are distinct but inseparable. It is Christ who is seen, but it is the Spirit who reveals him.
The effects of the Holy Spirit's coming upon the Apostles give us an idea of His work on the Church and in each individual. Throughout their long and difficult apostolic career, the Spirit sustained the first leaders of the Church. He inspired some of them and some of their disciples, to set down the Word of God in writing, thus increasing the written source of revelation. He strengthened them to give the final witness to the faith with the shedding of their own blood in martyrdom.
From these, we can better understand the work of the Spirit in the Church. He is the soul of the Church, abiding with her, operating in her. He gives life to the mystical body, and unites all its members to each other and to Christ with the common bond of grace. Because of this grace, which through the Holy Spirit is poured out upon the Church, the Spouse of Christ is rendered holy and spotless, and her children sanctified. It is also the Holy Spirit who makes the Church infallible. He continually animates and illumines the pope, bishops, and priests in their teaching office, and enlightens the faithful on the truths they hear. In times of persecution and danger, the Holy Spirit is specially active, raising up leaders to guide the Church safely through crises, instilling courage into the faithful that they might bear witness to the faith even at the cost of life itself.
The role attributed to the Spirit with regard to the individual Christian is of Sanctifier. It is through him that we are made children of God, at Baptism he comes into our souls with sanctifying grace and infuses into us also his marvelous gifts by which we are rendered capable of living the divine life. As long as we do not drive him out by sin, he remains within us, enlightening, strengthening, inducing us by inspirations to do good and to persevere in the path of virtue.
The presence of the Holy Spirit within us makes us the living temples of God. We should respect the presence of God within us by having recourse to him in frequent prayer, full of adoration and love. We should avoid not only mortal sins, but also even the least sin, which hurts him.
The name, titles, and symbols of the Holy Spirit. Holy Spirit is the proper name of the one we adore and glorify with the Father and the Son. Jesus called the Holy Spirit "Paraclete" when he proclaims and promises the coming of the Holy Spirit. The lord also calls the Holy Spirit "the Spirit of truth." Aside from the proper name of the Holy Spirit, the third person is also referred to as the Spirit of the promise, the Spirit of adoption, the Spirit of Christ, the Spirit of the Lord, the Spirit of God, and the Spirit of Glory.
Different things symbolize the Holy Spirit. The symbolism of water signifies the Holy Spirit's action in Baptism, since after the invocation of the Holy Spirit it becomes the effective sacramental sign of new birth. The symbolism of the anointing with oil also signifies the Holy Spirit, to the point of becoming a synonym for the Holy Spirit. While water signifies birth and the fruitfulness of life given in the Holy Spirit, fire symbolizes the transforming energy of the Holy Spirit's actions. The Holy Spirit is also symbolized by cloud and light, occurring together. The seal is a symbol close to that of anointing. The seal indicates the indelible effect of the anointing with the Holy Spirit in the sacraments of Baptism, Confirmation, and Holy Orders; the image of the seal has been used in some theological traditions to express the indelible character imprinted by these three unrepeatable sacraments.
The finger also symbolizes the Holy Spirit. It is by the finger of God that Jesus casts out demons. Lastly, the dove symbolizes the Holy Spirit. It is in the form of the dove that the Holy Spirit comes down upon Jesus and remains with Him.