Pure devotional service in Krsna consciousness is one because in pure devotional service there is no demand from the devotee to be fulfilled by the Lord. But generally people take to devotional service with a purpose. As stated in Bhagavad-gita, people who are not purified take to devotional service with four purposes. A person who is distressed because of material conditions becomes a devotee of the Lord and approaches the Lord for mitigation of his distress. A person in need of money approaches the Lord to ask for some improvement in his monetary condition. Others, who are not in distress or in need of monetary assistance but are seeking knowledge in order to understand the Absolute Truth, also take to devotional service, and they inquire into the nature of the Supreme Lord. This is very nicely described in Bhagavad-gita (7.16). Actually the path of devotional service is one without a second, but according to the devotees condition, devotional service appears in multifarious varieties, as will be nicely explained in the following verses.