Historically, most Christian “missions” have been focused on converting the “heathen” to Christianity, with social service and aide—medical care, building projects, and so forth—being looked at, at least in part, as a means to that end. But it is not always that way, nor obviously does it have to be. I have been told—by Rama Coomaraswamy, who knew her quite well—that Mother Teresa, for example, did not look on her work with the poor of Calcutta in this way, but instead recognized the truth and value of Hinduism, while simply helping the people who came her way.
As you know, I am all for dialogue and discussion between people of different faiths—provided each party fully accepts his own traditional dogmas—and it makes a certain amount of sense for Christians to talk about their religion with people who know nothing about it; but of course I also think that those Christians need to be prepared to listen and learn from the people they talk to about their own religious tradition. The problem is that it is seldom “a level playing field”. In other words, the missionaries have usually been trained to be spokesmen for Christianity, and any given Muslim or Hindu or Buddhist they meet may or may not have the training or mental equipment to explain his beliefs.
Some of the most interesting cases have been those where highly educated Christian missionaries, like the French Benedictine monk Henri Le Saux (1910-73), who went to India as a missionary, were able to meet their non-Christian equals (or superiors). Father Le Saux had an especially important encounter with the great Hindu jnanin master Ramana Maharshi, and became convinced that Hinduism and Christianity were merely two forms of an identical truth. The monk actually changed his name to the Sanskrit Abhishiktananda (meaning “Bliss of the Anointed One [i.e., Christ]), and lived in India for the rest of his life, no longer concerned about converting the people around him.