Please explain this sentence from the "Magic Barrel": "Love, I have said to myself, should be a by-product of living and worship rather than its own end."
This story deals with a man trying to best understand himself and his place in the world. That position is tied to his religious beliefs, and his desire to be both a rabbi and a true man of God. He puts strong emphasis on his need to be spiritual and devotes his life to cultivating the best relationship to God, the best spirituality that he can.
However, what Finkle struggles to understand is that spirituality can not come from study, but should come from life. He is able to comprehend that love is essential to his worship of God, but he tries to "create" that love. He studies hard to understand God, believing that this will show his love.
In this quote, Finkle is finally understanding the true nature of love, and therefore God. He realizes that to best worship, and best love, he must live in the world, interact with people, be a part of what God created. By doing this, love will grow in his heart and will a by-product of his worship - not the thing he gets at the end of worship.