By A. C. Bhaktivedanta Swami Prabhupada
Bhakti means spontaneous loving service. When a servant renders service to his master in consideration of monetary exchange, it is not loving service neither this hired service can come within the category of “Bhakti”.
When  a friend renders service to a fellow friend in consideration of obligation or in expectation of reward or as a matter of gratitude, it is no longer spontaneous loving service and therefore cannot be called “Bhakti”.
When a father loves his son in expectation of future reward or self satisfaction or a son loves his father in consideration of gain or gratitude, it is no longer a spontaneous loving service and it is out of the operation of “Bhakti”. Similarly when a wife loves her husband with a view to the inflated pocket of the husband or a husband loves the skin and complexion of his wife or in consideration of duty towards each other, it is no longer a spontaneous loving service.
During our stay in the material world we have to maintain a relation between a material thing and its owner; between a master and a servant; between a friend and a friend between a father or a mother and a child or between a husband and a wife or such similar extended relation between man to man, man to beast or man to nature and none of these categories of different relations can be termed as “Bhakti”.
No relation within this mundane affair is possible without a motive behind it and even though apparently we may meet some relativity’s without any motive behind them some sort of motive, may be in a lower or higher degree. As such “Bhakti” or spontaneous loving service can not be applied to any object within the world of three dimension but it is a thing which is absolute monopoly of the Personality of Godhead.
When there is a question of service, there is automatically the acceptance of one who is served and also a servant. The Master of the Almighty Godhead being omnipresent, His service or his servants are also omnipresent and as such “Bhakti” is also omnipresent. Omnipresent as the Personality of Godhead is “Bhakti” is a term which is transcendental to all mundane ideas of service with its ineffectiveness or inebrieties. The service of the mundane world has its selfishness, insufficiency, and ineffectiveness but  “Bhakti” is completely different from all such mundane ideas. “Bhakti” is self-sufficient eternal and independent. Nothing is helpful for attainment of “Bhakti” and nothing is determinative for discharge of “Bhakti”. She is herself the means and herself the end, in her pure state.
This “Bhakti” which is applicable to Godhead only is unalloyed devotion without any desire for reward. Service of Godhead with a view to gain something is not unalloyed “Bhakti”.
It is quite possible that the devotee while within the modes of material nature, will as a matter of course, perform his service to Godhead with some form or other of desire. These desires are divided into the modes of darkness, passion and goodness. Service of Godhead, with a desire of envy, pride, enmity, anger etc. which are the products of differentiation, is alloyed “Bhakti” in the mode of darkness. The example of such mixture of “Bhakti” in the mode of darkness, is set by those who offer prayers to Godhead for the annihilation of their enemies. Godhead need not be prayed specifically for the annihilation of ones enemies, for even though there is no prayer for such specific purpose, Godhead is always with his pure devotee to protect him from the hands of  the enemies. (to be continued)