Living in age when being “spiritual” is trendy and “religious” is old-fashioned, we may care to ask: How shall we become spiritual? I welcome the perspicacious answer from the Cappadocian theologian, Basil the Great (330-79): a person becomes spiritual through the indwelling of the Spirit. Once this occurs, we can experience the manifold power of the Spirit, which Basil memorably enumerates below:
Souls in which the Spirit dwells, illuminated by the Spirit, themselves become spiritual and send forth their grace to others. From here comes  foreknowledge of the future,  understanding of mysteries,  apprehension of what is hidden,  the sharing of the gifts of grace,  heavenly citizenship,  a place in the chorus of angels,  joy without end,  abiding in God,  being made like God and—the greatest of them all— being made God.
Imagine, the Spirit is the guarantor of my passport to Heaven, even reserving a spot in the chorus of angels that praises God for eternity. Imagine, the Spirit ensures that I possess “joy without end,” in contrast to happiness with an expiration date. Imagine, the Spirit not only makes me like God, as western Christians understand with the process of the sanctification, but goes even further and makes me God, as eastern Christians understand with the process of deification. No, I will not be identical to God, but I will conform to the image of Christ so much that my union with Him is seamless. I shall be “a little Christ.” Riffing on St. Athanasius, Lewis says the point of the incarnation is “the Son of God became a man to enable men to become sons of God,” and none of this is possible without the indwelling of the Spirit. Amazing stuff!