This is a misquote. Unfortunately, it is common in Buddhist circles that even the most senior teachers—or perhaps especially the most senior teachers—keep repeating the same debunked ideas. 
What the text says is, rather, that “this” mind is radiant, where “this” refers to the mind in jhana. The pali word idaṁ here serves to delimit and specify the mind in question.
The phrase Goldstein is referring to is, in Pali, found in two pairs of discourses, at AN 1.49–50 and in slightly expanded form at AN 1.51–52.
The context is crucial, because this portion of the canon, the Anguttara Ones, is entirely made up of sutta fragments; that is to say, discourses consisting of one or two sentences that have been splintered out from a full discourse in order to fill out the collection. In doing so, the context that gave them meaning has been stripped. With care and attention, though, it can be reconstructed to some degree.
In this particular case, the text has been stripped and divided in two at AN 1.51–60, then duplicated and fragmented again and placed in the previous chapter. When reading such texts, one must take extra care to consider the broader context. Think of our sutta fragment as an injured patient on life support. Almost everything is gone from it, so we would take super-duper care to ensure that nothing else is lost.
The text at AN 1.51 says this (my translation):
“This mind, mendicants, is radiant.
“Pabhassaramidaṁ, bhikkhave, cittaṁ.
But it is corrupted by passing corruptions.
Tañca kho āgantukehi upakkilesehi upakkiliṭṭhaṁ.
An uneducated ordinary person does not truly understand this.
Taṁ assutavā puthujjano yathābhūtaṁ nappajānāti.
So I say that the uneducated ordinary person has no development of the mind.”
Tasmā ‘assutavato puthujjanassa cittabhāvanā natthī’ti vadāmī”ti.
As the context makes clear, it is a text about “development of the mind”, i.e. the meditative practice otherwise known as samadhi or jhana. Words for “brightness”, “light” or 'luminosity" are constantly used by the Buddha to describe such a mind. The “defilements” obscure that brightness, like a pollutant in an oil lamp. This is taught, using the exact same terminology as the above fragment (pabhassara, upakkilesa) in such suttas as SN 46.33, AN 5.23, or AN 3.101, or MN 140.
The fact that this is part of a process of “development” shows that it cannot be something intrinsic or innate. The mind is not “naturally” radiant; it is “naturally” conditioned. But apparently the attachment to consciousness as a higher self runs so very deep that a single fragment can be snatched up and used to bolster the sense of self, despite everything the Buddha said about conditionality and impermanence.
In taking the phrase out of context and misquoting it, not only is an unwarranted sense imputed to the Buddha’s words, but the actual point he was making is lost. The phrases yathābhūtaṁ (“as it really is”, “truly”, “as it has been produced”) and “unlearned ordinary person” (contrasted with “noble disciple” in the next sutta) indicate that the passage is making a distinction between someone who has attained at least stream entry and someone who has not.
For those who are yet to realize the four noble truths, the nature of the mind is still unclear and the development of the mind is patchy and subject to regression. Thus the text says that for such a person there is no development of mind. Obviously this should not be taken to mean that an unenlightened person should not develop their mind (since that is taught many times elsewhere). Rather, it emphasizes the fragility of mental development before enlightenment, and reminds us that, while we may progress or regress, we have not really seen the causes and conditions until we have reached the noble fruits.
The message of the sutta is, then, that since the mind is conditioned, we must take special care that any progress in samadhi (“radiance”) does not falter due to the re-arising of defilements (upakkilesa). Such defilements are “passing” or “transient”, since they are temporarily suppressed in jhana and re-appear unexpectedly, though the meditator may think they have gone forever. Only with the attainment of noble insight will we really understand this process, after which our meditation will be much more stable.
the mind is a profound state of meditation that works on a different level than the usual one.