Saint Theresa of Avila

The devil will try to upset you by accusing you of being unworthy of the blessings that you have received. Simply remain cheerful and do your best to ignore the devil's nagging. If need be even laugh at the absurdity of the situation. Satan, the epitome of sin itself, accuses you of unworthiness! When the devil reminds you of your past, remind him of his future!

-- Saint Theresa of Avila

Saint Augustine of Hippo

Neither are the souls of the pious dead separated from the Church which even now is the kingdom of Christ. Otherwise there would be no remembrance of them at the altar of God in the communication of the Body of Christ.

-- Saint Augustine of Hippo from "The City of God"

Saint Thomas More

And, therefore, my own good daughter, do not let your mind be troubled over anything that shall happen to me in this world. Nothing can come but what God wills. And I am very sure that whatever that be, however bad it may seem, it shall indeed be the best. 

-- Saint Thomas More in a letter from prison to his daughter Margaret

Saint John of the Cross

Live in the world as if only God and your soul were in it; then your heart will never be made captive by any earthly thing. 

-- Saint John of the Cross