In this week's Parsha, the Torah refers to a man or woman who commits any sin by engaging in an act of treachery towards Hashem (במדבר ה':ו'). As apparent examples of this, the Torah immediately presents a number of seemingly unrelated laws, including the law of one who steals and then swears that he did not, the law of one who robs from a גר, a proselyte, and the law that the right to distribute certain forms of Terumah (tithes) belong to the owner of the produce exclusively. It is possible that the lesson which the Torah is trying to teach us here is that the reason that one may not steal is not merely because by taking something from another person, one is in effect "hurting" him, because if that were the only problem, then there would be many situations where this would in fact not be a problem at all, and stealing would therefore be allowed. For example, one could rationalize stealing from the rich (and swearing falsely about it afterwards), because that small loss of money would not hurt the rich person in the least. One could also rationalize stealing from a wealthy proselyte, for in addition to the fact that it does not hurt him because he is wealthy anyway, he also has no heirs who will lose by this theft. And one could also justify stealing Terumah and tithes, because the owner can not derive any personal pleasure from them and must give them away anyway. But all of these acts are nevertheless forbidden.
The Torah thus perhaps listed all these types of theft together in one place in order to teach us that the act of theft or robbery is not forbidden only because by stealing, one is hurting the victim. The sin actually is that the person is taking something that Hashem did not give to him. It is thus important for man to accept whatever he has, to ascertain whether what he has was really meant for him, and for him to desire only that which Hashem presents to him; a person must therefore strive to have only that which he has earned in a permissible and honest manner, and never try to rationalize taking what someone else has.