When set against the supernal, divine truth, there is no difference whatsoever between imagined faith and heresy
"Imagined faith" is faith that offers a representation of God, portraying God in one way or another. For more detail, see Poetry of Being by Yosef ben Shlomo, Chapter 3, "The Rational and the Irrational."
That is, like atheism, primitive representational faith is as far as can be from truth; in comparison with divinity, they are equally false.
In other words, from the point of view of divinity, there is no difference between primitive faith and atheism - both are wrong. But from the human point of view, they are wrong in different ways: one leans toward goodness and truth, the other toward evil and falsehood.
That is, the wicked stumble in the very place where the righteous pass.
Rather than to the level of the divine, as God created the world so that humanity could live and act in it.
That is, in relation to the light of the Infinite One, the difference is insignificant.
This is because atheism draws its spiritual strength from the rejection of primitive religiosity, which is, in essence, religious activity. The person who becomes a real, independent atheist is one whose spiritual demands are so high that that person does not tolerate primitive faith. For this reason, such a person's atheism contains within it the supernal radiance.
The words "transform bitterness to sweetness" were added in the 1983 edition to emphasize that atheism is not good in itself, but that people of a higher level of spirituality, who have become atheists purely because the religion they have been taught is too primitive for them (and they are therefore unable to accept it) extract from atheism sparks of a higher good, and in that way transform their lack of faith into elements of supernal light.