The suggestion is Dr. Charlton’s, and I believe it draws attention to the gaping chasm present in what falls under the umbrella of classical/traditional/conventional Christianity.
The reasons for Creation in traditional Christianity expound upon causes and their related ontological considerations and remain eerily silent when it comes to explicating the motivations for those causes and reasons.
Simply put, traditional Christianity was designed to render all questions about the motivation for Creation obsolete. Traditional Christianity is hardwired against the audacity of supposing God has any motivations for Creation at all. Creation is just something God does. He could not do otherwise.
In this sense, traditional Christianity is happy to inform you about the whats and hows but adamantly avoids considerations of the whys of Creation because it rejects the possibility of any why nots.
The supposed whys it does offer—God displaying his glory, creating all the good that can be created, etc—are merely what and hows in disguise.
Traditional Christianity offers no insights into potential motivations for Creation because it is grounded in secondary thought.
By its nature and limitations, secondary thought precludes all considerations of motivation because it can offer nothing more than causes and reasons, which inevitably all culminate in the one and only big eternal cause and reason.
Asking for anything beyond that point is considered absurd.
Secular materialism is also grounded in secondary thought. Like traditional Christianity, it offers its own explanations of causes and reasons, and like traditional Christianity, it essentially rules out the possibility of comprehending any sort of underlying motivation for the physical universe.
Secular materialism can tell you all about the Big Bang but will scornfully smirk at you if you dare ask it why the Big Bang occurred. The Big Bang (or string theory, or multiverse, or quantum this-or-that) is the only big cause or reason. Asking for anything beyond that point is absurd.
In the end, traditional Christianity and secular materialism offer remarkably similar non-answers when it comes to the matter of why or positing motives for Creation.
Neither acknowledges the question as a valid question.
And how could it be otherwise? After all, both are firmly grounded in secondary thought.
Both implicitly deny the reality of direct knowledge and primary thinking.
However, denials of reality do not negate reality.
Primary thinking and direct knowledge are real, and it is through them, and only through them that we can access the whys, the motives for God creating rather than not.
Note added: By extension, primary thinking and direct knowledge is the direction Christianity or, at the very least, individual Christians need to go.