Father Gabriel of St. Mary Magdalene, O.C.D. writes in Divine Intimacy:
Although our soul is supernaturalized by sanctifying grace, our powers [intellect and will] strengthened by the infused virtues [faith, hope, and charity], and our actions preceded and accompanied by actual grace, still the manner of our acting always remains human, and is therefore incapable of uniting us perfectly with God, of bringing us to sanctity.
This sounds pretty hopeless on the surface, but let us kneel before God in all humility and listen further:
In fact, our intellects, although invested with the virtue of faith, are always inadequate in regard to infinite Being, and are always incapable of knowing God as He really is. Even following the truths of revelation, which tell us that God is One and Three, the ideas which we form about the Most Holy Trinity, the three divine Persons, and the perfections of God, always remain far short of the reality.
As long as we are on earth, we shall know God "through a glass darkly"; only in heaven shall we see Him "face to face" (1 Cor. 13:12). [If St. Paul struggles with this, why should we be surprised at our own limitations? Or worse, how can we ever be over-confident in our own perceptions?]
The inadequacy of our knowledge of God extends equally to our ideas of sanctity; the same short-sightedness that characterizes our view of divine things affects our notions of the way of perfection. In many cases we cannot even discern what is more perfect, and despite our good will, we often make mistakes, believing some things to be good and holy which really are not. [Man's capacity for self deception seems to be infinite. It is the reality of being human.]
However, complete union with God, which is sanctity, requires a perfect orientation toward Him, according to the first and greatest commandment of Jesus: "Thou shalt love the Lord thy God with thy whole heart, and with thy whole soul, and with thy whole mind" (Mt. 22:37); we have seen that this perfect orientation exceeds our powers, precisely because our knowledge of God and of the way which leads to Him is far too imperfect.
"Must we then renounce sanctity? Not at all! God, who wants our sanctification, has provided us with the means of attaining it: He has given us the Holy Spirit.
I like to think of the Holy Spirit as "The Great Enabler" because He takes the desire the Father has written on our hearts from the moment of conception and facilitates our moving toward sanctity - union with God. He knows what we need far better than we do and He prompts us in the stillness of our hearts. He is indeed the Comforter Christ promised us before ascending into heaven. He is the divine life within us.
When we are anxious, confused, heartbroken over adversities or in spiritual darkness; when we think we will never be good enough for heaven or when we think God has abandoned us and we don't really matter to anyone, we can pray with St. Augustine:
O Love of the eternal God, sacred communication between the omnipotent Father and His blessed Son, all-powerful Paraclete, most merciful Consoler of the afflicted, penetrate the innermost depths of my heart with Your powerful virtue; brighten with Your shining light any dark corners of that neglected dwelling of my soul. Visit it, fructifying with the abundance of Your dew, all that a long period of drought has dried up and choked. Pierce with the dart of Your love, the depths of my soul; penetrate the very center of my enervated heart and inflame it with Your salutary fire; strengthen Your creature by illumining, with the light of Your holy fervor, the inmost depths of my mind and heart.
I believe that each time You come into a soul, You prepare there a dwelling for the Father and the Son. Blessed is he who is worthy to have You as Guest! Through You, the Father and the Son establish their dwelling in him. Come then, most benign Consoler of suffering souls, Protector in all circumstances and Support in tribulations. Come, Purifier of faults, Healer of the wounded. Come, Strength of the weak, Restorer of those who fall! Come Master of the humble, rejecter of the proud! Come, O charitable Father of orphans, merciful Judge of widows! Come, hope of the poor, strength of the weak! Come, guiding star of sailors, harbor of the shipwrecked! Come, O unique beauty of all the living, and only salvation of the dying!
Come, O Holy Spirit, come and take pity on me! Clothe me with Yourself, and graciously hear my prayers, that, according to the multitude of Your mercies, my littleness may be pleasing to Your greatness, and my weakness to Your strength, through Jesus Christ, my Savior, who, with the Father, lives and reigns in unity with You, forever and ever. Amen."