From the treatise On the Holy Spirit by Saint Basil the Great, bishop (330 – January 1, 379 AD)
The Work of the Holy Spirit
The titles given to the Holy Spirit must surely stir the soul of anyone who hears them, and make him realize that they speak of nothing less than the supreme Being. Is he not called the Spirit of God, the Spirit of truth who proceeds from the Father, the steadfast Spirit, the guiding Spirit? But his principal and most personal title is the Holy Spirit.
To the Spirit all creatures turn in their need for sanctification; all living things seek him according to their ability. His breath empowers each to achieve its own natural end.
The Spirit is the source of holiness, a spiritual light, and he offers his own light to every mind to help it in its search for truth. By nature the Spirit is beyond the reach of our mind, but we can know him by his goodness. The power of the Spirit fills the whole universe, but he gives himself only to those who are worthy, acting in each according to the measure of his faith.
Simple in himself, the Spirit is manifold in his mighty works. The whole of his being is present to each individual; the whole of his being is present everywhere. Though shared in by many, he remains unchanged; his self giving is no loss to himself. Like the sunshine, which permeates all the atmosphere, spreading over land and sea, and yet is enjoyed by each person as though it were for him alone, so the Spirit pours forth his grace in full measure, sufficient for all, and yet is present as though exclusively to everyone who can receive him. To all creatures that share in him he gives a delight limited only by their own nature, not by his ability to give.
The Spirit raises our hearts to heaven, guides the steps of the weak, and brings to perfection those who are making progress. He enlightens those who have been cleansed from every stain of sin and makes them spiritual by communion with himself.
As clear, transparent substances become very bright when sunlight falls on them and shine with a new radiance, so also souls in whom the Spirit dwells, and who are enlightened by the Spirit, become spiritual themselves and a source of grace for others.
From the Spirit comes foreknowledge of the future, understanding of the mysteries of faith, insight into the hidden meaning of Scripture, and other special gifts. Through the Spirit we become citizens of heaven, we enter into eternal happiness, and abide in God. Through the Spirit we acquire a likeness to God; indeed, we attain what is beyond our most sublime aspirations—we become God.
From the dogmatic constitution on the Church of the Second Vatican Council When the Son completed the work with which the Father had entrusted him on earth, the Holy Spirit was sent on the day of Pentecost to sanctify the Church unceasingly, and thus enable believers to have access to the Father through Christ in the one Spirit. He is the Spirit of life, the fountain of water welling up to give eternal life. Through him the Father gives life to men, dead because of sin, until he raises up their mortal bodies in Christ. The Spirit dwells in the Church and in the hearts of the faithful as in a temple. He prays in them and bears witness in them to their adoption as sons. He leads the Church into all truth and gives it unity in communion and in service. He endows it with different hierarchical and charismatic gifts, directs it by their means, and enriches it with his fruits. By the power of the Gospel he enables the Church to grow young, perpetually renews it, and leads it to complete union with its Bridegroom. For the Spirit and the Bride say to the Lord Jesus: "Come!" In this way the Church reveals itself as a people whose unity has its source in the unity of Father, Son and Holy Spirit. The whole company of the faithful, who have an anointing by the Holy Spirit, cannot err in faith. They manifest this distinctive characteristic of theirs in the supernatural instinct of faith (sensus fidei) of the whole people when, from the bishops to the most ordinary lay person among the faithful, they display a universal agreement on matters of faith and morals. This instinct of faith is awakened and kept in being by the Spirit of truth. Through it the people of God hold indefectibly to the faith once delivered to the saints, penetrate it more deeply by means of right judgment, and apply it more perfectly in their lives. They do all this under the guidance of the sacred teaching office: by faithful obedience to it they receive, not the word of men but in truth the word of God. Moreover, the Holy Spirit not only sanctifies and guides God's people by the sacraments and the ministries, and enriches it with virtues, he also distributes special graces among the faithful of every state of life,assigning his gifts to each as he chooses. By means of these special gifts he equips them and makes them eager for various activities and responsibilities that benefit the Church in its renewal or its increase, in accordance with the text: To each is given the manifestation of the Spirit for a good purpose. These charisms, the simpler and more widespread as well as the most outstanding, should be accepted with a sense of gratitude and consolation, since in a very special way they answer and serve the needs of the Church.
The mission of the Holy Spirit in the Church