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.
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.
Through the Spirit we become citizens of heaven, we are admitted to the company of the angels, 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 St. Basil the Great