As an introduction to פרשת קדושים, Rabbeinu Bechaye discusses the challenge that one has in overcoming his תאוה. This word is generally translated as lust or desires.
It really refers more to types of obsessions where the individual really struggles to overcome them.
Rabbeinu Bechaye says that תאוות can come in four ways: בגופו, with his physical body and refers to lusting after women forbidden to him. It includes overcoming improper sexual urges.
The second is במאכלו, with food. This can include forbidden foods or an overall obsession with eating. One needs to conquer this תאוה as well.
The third is דיבורו, speech. Some have a difficult time to overcome their desire to gossip and speak לשון הרע. They got some satisfaction in bad mouthing people. This, too must be overcome.
And the fourth תאוה is במחשבתו, with one’s thoughts. Some find it difficult to maintain pure thoughts throughout the day. It is also important to drive away negative thoughts that bring us down. Worrying is also included in negative thinking.
The ultimate goal is קדושה. If one can overcome his תאוה in these four areas, he will be successful in achieving the ultimate goal of קדושה, holiness.