When the Torah tells us about the prohibitions of seeking answers about the future through sorcery, it says in the Pasuk, "Tamim te'iyeh im Hashem Elokecha - You should have a perfect (faith) with Hashem your G-d". The Torah is teaching us not to worry about the future and instead trust in Hashem with a "perfect" faith, that He is taking care of us and knows what He is doing. When we seek answers about the future on our own, it shows that we are trying to take control of our own destiny and are not trusting enough in Hashem.
The word Tamim is also used in reference to Shmiras Habris. Noach was called a Tzadik Tamim. Chazal say that Tamim refers to the fact that he was gadur from arayos. Also, when Hashem introduced the mitzva of Mila to Avraham Avinu he prefaced it with the words "Hishalech lifanai ve'heyei Tamim". How does the word "Tamim" (which implies a perfect faith) tie in with Shmiras Habris?
Perhaps we can explain it as follows. When a person looks at other women or pursues forbidden pleasures, what he is really feeling deep down is that Hashem doesn't provide him with all he needs and he therefore takes his needs into his own hands, by either looking at that which isn't his or by indulging in pleasures that weren't given to him by Hashem. In order for us to be Shomer Habris, we must let go of control and develop a "perfect faith" that Hashem is providing all our needs. The pleasures that we sometimes feel we need so much, we DON'T really need. If they were true needs, Hashem would have given them to us - or permitted them to us.
Yes, we CAN let them go. Hashem is taking perfect care of us. He doesn't need our help at all.
And indeed, we find that the more a person tries to take his own needs into his hands, he starts to LOSE that which Hashem had previously provided him. Many people report losses in Parnassa, Nachas, Shalom Bayis, Inner Peace, and so many other important things. This is a direct message from Hashem - mida kineged mida - that if we think we will take our needs into our own hands, Hashem will show us which needs are REALLY important, and WHO is it that was REALLY providing our needs all this time.
The more we let go of our "perceived needs" and TRUST in Hashem to care for us, the more we allow the light of Hashem to flow through us and bring true blessing into our lives.
Developing a "perfect faith" is not an overnight event, but that we need to constantly grow in that direction... TAMIM TEIYEH IM HASHEM ELOKECHA is the underlying secret to Shmiras Habris, and perhaps this is why it is so important in the life of a Yid.
