Chosen lady: this is the way John greets the community of an unknown city. The Church is chosen and holy, just as the people in it are the chosen and holy ones of God.
John invites the people to have a steadfast and emphatic attitude toward those who do not accept the faith of the apostles. At the same time he reminds them of the fundamental law for Christians: love.
To remain zealously faithful to the Truth is to love Christ who entrusted this truth to us. We need the whole truth and not only what is most pleasing to people today.