In Chulin 7b, Rabbi Chanina ben Dosa was not concerned with the threats of a sorcereress due to his understanding that "Ain od Milvado (Devarim 4:35)" included even the powers of sorcery. What was his source for this, and is it incumbent to understand it as such even today?
The Rambam explains that the ideology behind sorcery is idolatry. They are believing that there are other powers that can be placated or coerced to fulfill your desires.
The Gemara there, in Chulin 7b, says that the term Kishuf chimes from the fact that these powers are working against the heavenly order.
Rebbe Chanina is saying that only Hashem is in charge and anything else is a facade.
The Gemara ends up saying that for most of us sorcery does have an effect, but for the likes of Rebbe Chanina, who saw so clearly how Hashem is in charge, it can't have an effect.
To understand this a little better, the Maharal in Be'er Hagoleh explains that when the Gemara says that reciting Krias Shema gets rid of other forces, this is because you are reaffirming Hashem as the only One in control. This causes the facade of other powers to fade.
To answer the second question, the Gemara ends up saying that sorcery can have have an effect. But you can take this verse all the way to its fullest meaning and if you truly accept that then it will be true to you.