The most striking proof that there is a devil in the world is that men do not feel, or feel very little (though some endeavour to do so), the mercies that God has bestowed upon them in the creation, guidance and redemption: the Devil is a powerful antagonist to everything good and righteous.
The problem of our life is union with God, and sin completely prevents this; therefore flee from sin as from a terrible enemy, as from the destroyer of the soul, because to be without God is death and not life. Let us therefore understand our destination; let us always remember that our common Master calls us to union with Himself.
It is especially necessary for Christians to have a pure heart, so that they may be able to see God with the eyes of the heart, as He is, with His love to us and with all His perfections, as well as to be able to contemplate the beauty of the angels, all the glory of the Holy Virgin, the beauty of Her soul and Her greatness, as the Mother of God, and the beauty of the souls of God’s saints, and their love to us; we must see them as they are in themselves, we must contemplate the truths of the Christian faith, with all its sacraments, and feel their greatness; we must see the state of our own souls, and especially our sins. An impure heart–that is, a heart occupied with earthly passions–feeds itself on the carnal desires of the eyes and worldly pride; it cannot see any of the things we have indicated.
Is it possible to pray rapidly without injuring the effect of the prayer? It is possible to those who have learned to pray inwardly with a pure heart. During prayer it is necessary that your heart should sincerely desire that which you ask for, should feel the truth of what you are saying, and this comes naturally to a pure heart. That is why it is capable of praying even rapidly, and at the same time agreeably, to God, as the rapidity in this case does not injure the truth (sincerity) of the prayer. But for those who have not attained the capability of praying sincerely it is necessary to pray slowly, waiting for a corresponding echo in the heart to each word of the prayer. And this is not always soon given to men unaccustomed to prayerful contemplation. Therefore, for such men, it must be laid down as an absolute rule to pronounce the words of the prayer slowly, and with pauses. Wait until every word gives back its corresponding echo in your heart.
Sometimes in his heart a man draws near to God, sometimes he goes far from God, and therefore he experiences either peace and joy, or fear, disturbance, and oppression. The one is life, the other spiritual death. We draw near to God mostly in time of affliction, from which no one can save us but God, to Whom we then turn with our whole heart, and thus approach Him sincerely; whilst we go far from God in times of ease and abundance of earthly blessings, which make the old carnal man proud of himself, and–especially when he thirsts for riches, glory and distinction, and has attained all these–he loses faith from his heart and forgets God, his Judge and Recompenser, forgets the immortality of his soul, and his duty to love God with all his heart and his neighbour as himself.
From My Life in Christ .