While we live here we should use all temporal goods and physical necessities the way a guest does in a strange place where he stays overnight and leaves in the morning. He needs no more than bed and board and need not say: This is mine; here I will stay. Nor dare he take possession of the property as though it belonged to him by right; otherwise he would soon hear the host say to him: My friend, don't you know that you are a guest here? ... The temporal goods you have God has given to you for this life. ... But you should not hang your heart on them as though you were going to live forever. You should always go on and consider another, higher, and better treasure, which is your own and which will last forever.
What Luther Says - #4307 - p. 1340