1. Materialism and bhakti — you can’t have both

    Krsna consciousness, or bhakti, devotional service, means to develop attachment for Krsna and in the same proportion develop detachment for material sense gratification. Two things cannot go on. Just like here is a glass containing water. If you want to put milk in this glass, then you have to throw away the water. If you think that "I shall keep half water, half milk," that can be done, but both of them becomes diluted or polluted. If you want to keep milk, then you have to throw out the water, and if you want to keep water, then you cannot keep milk. Similarly, bhakti paresanubhavah. This is the test. If you become Krsna conscious, if you are improving in spiritual life, proportionately you'll be detached from materialistic way of life. That is the test. Simply thinking that "I am meditating so much, I am making very good advance," is not. You have to test. The test is that your… Improvement of spiritual life means that you become detached to the materialistic way of life. Bhaktih paresanubhavo viraktir anyatra syat [SB 11.2.42].

    From Srila Prabhupada's lecture on Bhagavad-gita 2.40-45 — Los Angeles, December 13, 1968