The one thing necessary - The interior life ... is something far more profound and more necessary in us than intellectual life or the cultivation of the sciences, than artistic or literary life, than social or political life. Unfortunately, some great scholars, mathematicians, physicists, and astronomers have no interior life, so to speak, but devote themselves to the study of their science as if God did not exist. In their moments of solitude they have no intimate conversation with Him. Their life appears to be in certain respects the search for the true and the good in a more or less definite and restricted domain, but it is so tainted with self-love and intellectual pride that we may legitimately question whether it will bear fruit for eternity. Many artists, literary men, and statesmen never rise above this level of purely human activity which is, in short, quite exterior. Do the depths of their souls live by God? It would seem not.
This shows that the interior life, or the life of the soul with God, well deserves to be called the one thing necessary, since by it we tend to our last end and assure our salvation. This last must not be too widely separated from progressive sanctification, for it is the very way of salvation.