"Men loved darkness instead of light because their deeds were evil. Everyone who does evil hates the light, and will not come into the light for fear that his deeds will be exposed. But whoever lives by the truth comes into the light, so that it may be seen plainly that what he has done has been done through God" (Jn. 3:19-21).
Missionaries working in a foreign country were attempting to get the natives to practice better sanitation. They showed them some water from a sacred river under a microscope in order to warn them of the filth and disease it contained. The natives responded by stealing the microscope and destroying it.
Whenever the sin of those who love darkness is revealed, the reaction is the same. The messenger is shot, because the revealing news he or she brings is not welcome. Prophets are always opposed and persecuted, and sometimes they are killed. The same reaction is even present to a lesser degree amongst those who walk in the light. Sometimes we get too comfortable in our usual ways of doing things and with our inherited patterns of thought, so that we do not like anyone to challenge us to think anew or to look at things from a different perspective. An open investigation in the "light" is sometimes prevented by the kneejerk accusation: "That's liberal" or "That's ______________" (fill in the blank as appropriate).
It is for this reason that many people rejected Jesus when he appeared in this world, because they were expecting someone different. Some of those who opposed Jesus were doing so from the best of intentions. They thought that they were preserving truth against his innovative error. They refused to admit that their reasoning and cherished positions might be wrong. Therefore, they never gave Jesus a fair hearing.
Part of what it means to be one who "lives by the truth" is to have a willingness to put things to the test, to question, to ask, and to have an open mind. One who "lives by the truth" is not afraid of honest investigation, because that person is not afraid of the "light."