You want me to tell you why God is to be loved and how much. I answer, the reason for loving God is God Himself; and the measure of love due to Him is immeasurable love. Is this plain? Doubtless, to a thoughtful man; but I am debtor to the unwise also. A word to the wise is sufficient; but I must consider simple folk too. Therefore I set myself joyfully to explain more in detail what is meant above.
We are to love God for Himself, because of a twofold reason; nothing is more reasonable, nothing more profitable. When one asks, Why should I love God? he may mean, What is lovely in God? or What shall I gain by loving God? In either case, the same sufficient cause of love exists, namely, God Himself.
And first, of His title to our love. Could any title be greater than this, that He gave Himself for us unworthy wretches? And being God, what better gift could He offer than Himself? Hence, if one seeks for God's claim upon our love here is the chiefest: Because He first loved us (I John 4.19).
St. Bernard of Clairvaux, On Loving God