In the literal sense the pasuk is telling us not to follow the diviners of auspicious time and soothsayers b/c לא כן נתן לך השם א-להיך - Hashem didn't give you things like these.
Rav Simcha Bunim explained לא "כן" נתן לך השם א-להיך - Hashem didn't give you "כן" - Like this. That things should be done in a certain way and no other. Sometimes you do things one way but if you have to make changes or modifications you refrain from doing so. Some people are very rigid in their behaviors. They have to learn flexibility.
The context of the pasuk is Avoda Zara teaching that it is actually a subtle form of Avoda Zara to always insist on doing things a certain way. It is not Hashem one is serving but oneself... [The Kotzker expressed this idea].
"לא כן נתן לך השם א-להיך"! Be flexible!!
