80. Nothing that we simply think about becomes part of us, even though we think we intend to do it, unless we intend it to the point that we would actually do it if the opportunity arose. This is because when we do things for this reason, from intent with the aid of discernment or from a desire of intent with the aid of thought from discernment, then we really do them. As long as it is a matter of thought alone it cannot be made part of us, because our discernment does not unite itself to our volition, or the thinking of our discernment to the desire of our intent. Our intent and its desire, though, do unite themselves to our discernment and its thinking, as has been amply explained in part 5 of Divine Love and Wisdom.
This is the intent of the Lord's words, "It is not what goes into peoples' mouths that makes them unclean; rather, what comes out through the mouth from the heart makes them unclean" (Matthew 15:11, 17-18, 19). Spiritually understood, "the mouth" means our thought, because thought is expressed through the mouth, and "the heart," spiritually, means the desire that comes from love. If this is the source of what we think and say, then it makes us unclean. In Luke 6:45 as well, "the heart" means the desire that comes from love or volition and "the mouth" means the thought of our discernment.
(References: Matthew 15:17-19)