Answer: truth
Step-by-step explanation:
There are two main points in the second epistle of John: "truth" and "love". Love refers to keeping the commandments of God, while truth refers to the danger of encouraging false teachers.
Walking in obedience to God´s commands is the definition of love, as love equals obedience to the truth. There´s a warning about deceivers, who do not acknowledge Jesus Christ, and therefore, are not walking in obedience nor speaking truth.