St. John, no doubt, would have given the world to follow, recall, retain her, when she thus left him; but he would not give one chance of heaven, nor relinquish, for the elysium of her love, one hope of the true, eternal Paradise.
– Charlotte Bronte
Jane Eyre, Chapter 32. St. John refuses to marry Rosamond even though they love each other. He simply cannot envisage her settling down to missionery life with him in India, a path he intends to follow. For him the love he will experience serving God is more important than human love.