“If anyone comes to you and does not bring this teaching, do not take them into your house or welcome them. Anyone who welcomes them shares in their wicked work.” (2 John 10-11)
It is not uncommon for Christians to think this passage forbids them from inviting LDS missionaries into their homes. At first glance it is easy to see why. A closer look, however, reveals that this is not its intent.
A hallmark of good biblical interpretation is to interpret passages in their historical context. Much damage has been done to many passages by not taking their context into account. In John's day, there weren't people like Mormon missionaries going door to door trying to spread their doctrine. When traveling preachers came to somebody's door it was to gain support from them. They were looking for a place to stay and other means of support. Jesus referred to this practice when he sent the twelve on a mission trip and told them: “Whatever town or village you enter, search there for some worthy person and stay at their house until you leave” (Matthew 10:11).
That this was also the situation John addresses in 2 John is seen from what he writes in 3 John. There John writes to Gaius thanking him for his service. Especially pertinent are verses 5-8 where we learn that Gaius showed hospitality to orthodox teachers. Note how John views this as Gaius and the teachers working together for the truth.
Dear friend, you are faithful in what you are doing for the brothers and sisters, even though they are strangers to you. They have told the church about your love. Please send them on their way in a manner that honors God. It was for the sake of the Name that they went out, receiving no help from the pagans. We ought therefore to show hospitality to such people so that we may work together for the truth.
A parallel situation today is not that of LDS missionaries coming to the door, but of false teachers soliciting money for their ministries. God doesn’t want us to support false teachers - either with financial support or with a blurring of the differences in teaching. A respected theologian summed up well the meaning of 2 John 10-11: "We are not forbidden to hold friendly, civil intercourse with him. What is forbidden is to greet such a one, and deal with him, as a brother in the faith." (Francis Pieper, Christian Dogmatics, Vol. 1. p. 569)