Saint Basil the Great.
That is why the Lord taught the Samaritan woman, who thought that God had to be worshipped in specific places, that “God is Spirit”. He wanted to show that an incorporeal being cannot be circumscribed. When we hear the word "spirit" it is impossible for us to conceive of something whose nature can be circumscribed or is subject to change or variation, or is like a creature in any way. Instead, we are compelled to direct our thoughts on high, and to think of an intelligent being, boundless in power, of unlimited greatness, generous in goodness, whom time cannot measure. All things thirsting for holiness turn to Him; everything living in virtue never turns away from Him. He waters them with His life-giving breath and helps them reach their proper fulfillment. He perfects all other things, and Himself lacks nothing; He gives life to all things, and is never depleted. He does not increase by additions, but is always complete, self-established, and present everywhere. He is the source of sanctification, spiritual light, who gives illumination to everyone using His powers to search for the truth - and the illumination He gives is Himself. His nature is unapproachable; only through His goodness are we able to draw near it. He fills all things with His power, but only those who are worthy may share it. He distributes His energy in proportion to the faith of the recipient, not confining it to a single share. He is simple in being; His powers are manifold: they are wholly present everywhere and in everything. He is distributed but does not change. He is shared, yet remains whole. Consider the analogy of the sunbeam: each person upon whom its kindly light falls rejoices as if the sun existed for him alone, yet it illumines land and sea, and is master of the atmosphere.
In the same way, the Spirit is given to each one who receives Him as if He were the possession of that person alone, yet He sends forth sufficient grace to fill all the universe. Everything that partakes of His grace is filled with joy according to its capacity - the capacity of its nature, not of His Power.
The Spirit does not take up His abode in someone's life through a physical approach; how could a corporeal being approach the Bodiless one?. Instead, the Spirit comes to us when we withdraw ourselves from evil passions, which have crept into the soul through its friendship with the flesh, alienating us from a close relationship with God. Only when a man has been cleansed from the shame of his evil, and has returned to his natural beauty, and the original form of the Royal Image has been restored in him, is it possible for him to approach the Paraclete. Then, like the sun, He will show you in Himself the image of the invisible, and with purified eyes you will see in this blessed image the unspeakable beauty of its prototype. Through Him hearts are lifted up, the infirm are held by the hand; and those who progress are brought to perfection. He shines upon those who are cleansed from every spot, and makes them spiritual men through fellowship with Himself. When a sunbeam falls on a transparent substance, the substance itself becomes brilliant, and radiates light from itself. So too Spirit-bearing souls, illumined by Him, finally become-spiritual themselves, and their grace is sent forth to others. From this comes knowledge of the future, understanding of mysteries, apprehension of hidden things, distribution of wonderful gifts, heavenly citizenship, a place in the choir of angels, endless joy in the presence of God, becoming like God, and, the highest of all desires, becoming God. These are only a few of the many things we have been taught concerning the greatness, dignity, and working of the Holy Spirit, and we have learned them from the Spirit's own words.
Reference:
St. Basil the Great, On the Holy Spirit, St. Vladimir’s Seminary Press, Crestwood, New York 10707 (1980).