Srila Prabhupada..."Just like one of my German Godbrothers said that in Germany during the last war, Second World War, many women used to go to the church to pray to God to get back their husband, son, or brother. But nobody came back. And they became atheist: "There is no God. We prayed so much, and my father did not come, my brother did not come, my son did not come." So motivated devotion is sometimes frustrated, and they become atheist.
Therefore the devotee who has no motive is pure devotee. "In any condition, it is my duty to love God and to serve Him, not for my benefit but God's satisfaction." That is pure devotee. "
Srila Prabhupada's Room Conversation with three Trappist Monks, Psychologists from the University of Georgia, and Atlanta Lawyer, Michael Green