St. Antony the Great: Endeavor to possess only the Kingdom

 Let us endeavor to possess nothing except what we shall take with us to the grave, namely, charity, meekness, righteousness and so on. Virtue, that is to say, the Kingdom of Heaven, needs only our good will, for it is within us. Actually, it consists simply in keeping the spiritual part of our soul in the purity and beauty in which it has been created.

+St. Antony the Great, from The Life of St. Antony, by St. Athanasius.

St. John Chrysostom: Mind the things of heaven

Instead of the things on earth, the cheap things which rush past and are gone, mind the things that are above, the things in heaven, the indestructible things, the things which coextend with eternity, the things which are seen by the eyes of faith, the things that know no end or succession, the things that have no boundary. I wish you constantly to keep your minds on these things. Our concern for them frees us from earth and transports us to heaven.
This is why Christ said: "Where a man's treasure is, there also is his heart" (cf Matt 6:21). For when the soul gets an understanding of the ineffable goods of heaven, it is, as it were, loosed from the bonds of the flesh and lifted on high. Each day it pictures to itself the enjoyment of these goods and can take no thought for the things on earth.
+St. John Chrysostom, from Baptismal Instructions, Instruction 7 #14-15.