How mistaken are those people who seek happiness outside of themselves, in foreign lands and journeys, in riches and glory, in great possessions and pleasures, in diversions and vain things, which have a bitter end! In the same thing to construct the tower of happiness outside of ourselves as it is to build a house in a place that is consistently shaken by earthquakes. Happiness is found within ourselves, and blessed is the man who has understood this. Happiness is a pure heart, for such a heart becomes the throne of God. Thus says Christ of those who have pure hearts: “I will visit them, and will walk in them, and I will be a God to them, and they will be my people.” (II Cor. 6:16) What can be lacking to them? Nothing, nothing at all! For they have the greatest good in their hearts: God Himself!
(St. Nektarios of Aegina, Path to Happiness, 1)
The soul that loves God has its rest in God and in God alone. In all the paths that men walk in in the world, they do not attain peace until they draw nigh to hope in God.
(St. Isaac the Syrian, Homily 56, 89)