We hear so much about people converting from one religion to another. Srila Prabhupada in his introduction to the Bhagavad Gita says that conversion of faith is material where as the dharma of all living entities is eternal. In other words, even if a person converts, still his dharma remains constant and eternal.
If a person is seeking God to serve God, then there is no need to convert from one religion to another.But if a person is seeking happiness (material or spiritual) in God, then such a person will convert. To serve God with no motive and no break in time is the ultimate dharma for mankind. Such selfless and timeless service can be conducted under any religious banner be it Christianity, Islam, Judaism or Krishna.
Most often than not, the institutional form of religions do not teach such selfless service to God, but however, propagate self-preservation and self-happiness in the name of God as the ultimate goal of life. Because there is lot of customer base for self-preservation and happiness in this world, institutionalized religions are competing with each other using mundane tactics to pull these customers to their institutions. This competitive pulling of customers from one religion to another is called conversion. Such conversions have no real basis in true dharma. It is an illusion!
Real dharma for all living beings is to serve God without any ulterior motive and without any break in time. One can do this in any setting any where!