But do you ask, dearly beloved, how a man may know whether he has the Spirit of God? If you truly know God , then you may be sure you have his Spirit. If, as the apostles say, no man knows the things of God save the Spirit of God, how can we know God unless we have his spirit? You may, however well wonder whether you know God... The spirit of the world which tempts men to scorn the divine commandments, to engage with pleasure in earthly affairs, to seek the heights of worldly domination, to submit to the shameful passions of fleshy delight, to increase their material possessions, and to strive after power over their fellows in their swollen pride. But the spirit which is of God urges all the souls he fills toward heavenly things, casts out the chill of negligence and of the flesh and kindles them to love of God, restrains the wanton desires of the body, and raises up the heart, having freed it from all earthly delights. By him men are made unyielding in their scorn of material prosperity and strong in overcoming obstacles; it makes the humbly subject to the good but cause them to oppose unbendingly, by right of their authority, those who do evil; this Spirit inebriates those whom it fills.
Saint Peter Damian, Doctor of the Church