Pope St. Gregory I was a Doctor of the Church who exercised influence in the shaping of Christian doctrine in both East and West. He was born at Rome about 540 and died in March 604. He is known as Saint Gregory the Great and as Saint Gregory the Dialogist. What follows is a sermon he preached in 604 A.D. It is rich food for thought, but not readily available, so I'm posting it here.
In the world, yet not of it
I would like to urge you to forsake everything, but that I do not presume to do. Yet, if you cannot give up everything of this world, at least keep what belongs to the world in such a way that you yourself are not kept prisoner by the world. Whatever you possess must not possess you; what you own must be under the power of your soul; for it your soul is overpowered by the love of this world's goods, it will be totally at the mercy of its possessions.
In other words, we make use of temporal things, but our hearts are set on what is eternal. Temporal goods help us on our way, but our desire must be for those eternal realities which are our goal. We should give no more than a side glance at all that happens in the world, but the eyes of our soul are to be focused right ahead; for our whole attention must be fixed on those realities which constitute our goal.
Whatever is vicious must be utterly eradicated, wrenched away not merely from being put into action but even from being so much as thought of. No carnal pleasure, no worldly curiosity, no surge of ambition must keep us from the Lord's supper. But further, our minds should merely skirt even the good deeds we perform in this life; in this way, the physical things which give us pleasure will serve our bodily needs without hindering the soul's progress. You see, my brothers, I dare not say to you, give up everyting. Yet, if you will, you can give up everything even while keeping it, provided you handle temporal things in such a way that your whole mind is directed toward what is eternal. A man can use the world as if he were not using it, if he makes all external needs minister to the support of his life without allowing them to dominate his soul. They remain external to him and under his control, serving him without halting the soul's drive to higher things. For such men, everything in this world is there for their use, not to be desired. Nothing should interfere with your soul's longing; no created pleasure in the world should ensnare you.
If the object of love is what is good, then the soul should take its delight in the higher good, the things of heaven. If the object of fear is evil, then we should keep before ourselves the things that are eternally evil. In this way, if the soul sees that we should have a greater love and a greater fear about what concerns the next life, it will never cling to this life.
To help us achieve all this we have the help of the mediator between God and Man. Through Him we shall obtain all this the more quickly, the more we burn with a great love for Him, who lives and reigns with the Father and the Holy Spirit, for ever and ever. Amen.
The text of this sermon (B1556) and other wonderful sermons by Pope Gregory can be found here.