In addition to this law of using multiple witnesses, another time-tested law of Bible study is that we should not base a teaching - and especially a doctrine - on the meaning of a Greek or Hebrew word. One reason is that a given word can have a multitude of meanings, depending on the context. Concordances are not menus that we pick from according to our preference, or according to a conclusion that we desire.
Another reason not to base a doctrine on the meaning of a word is that languages change over time, and modern Greek and Hebrew can differ significantly from biblical Greek and Hebrew. The exact meaning of a word in ancient times is not always certain, and therefore, more is required than looking up a word in a concordance or other study aid. Lexicons and Biblical dictionaries can help, but they are just that - a help, not a solid base. They have their place, certainly, but their definitions must be tested against biblical usage.
If you have been in the church for any length of time, you've probably observed that resting a teaching on the meaning of a word leads to arguments about words, which Paul warns against (I Timothy 6:4). Instead of meaningful discussions about the whole counsel of God, this approach encourages heaping up teachers (II Timothy 4:3) - such as scholars or reference works - that agree with a specific definition. Yet this is dangerous, because you can find support among scholars for almost any perspective, even ones that are anti-God.
But the most important reason not to base a doctrine on the definition of a word is that the definition only constitutes a single witness. Such a solitary testimony is not valid, as Jesus Himself establishes. A solid foundation consists of multiple witnesses that do not contradict the rest of the Word of God.
