Lucifer the Light bearer. Strange and mysterious name to give to the Spirit of Darkness. Lucifer the Son of the Morning. Is it he who bears the Light and with its splendors intolerable blinds feeble sensual or selfish souls? Doubt it not!
Now, Pike is a scholar of esoteric interpretation of the highest order, so I'm absolutely unqualified to fully unpeel that, and the context from the book and from the degrees is certainly necessary, but here's my personal views just based on the quote alone:
Lucifer the Light bearer.
This is simply a translation of the Latin word, derived from lux ferre which literally means "to bring light". There's no interpretation at all, here.
Strange and mysterious name to give to the Spirit of Darkness.
This isn't all that deep, interpretation-wise. It is strange that the spirit of darkness has a name which relates to Light. In the Bible, Light almost always refers to the divine, starting in the very first passage of Genesis.
Is it he who bears the Light
Now Pike is getting into deeper symbolic waters. He's introducing the double meaning of "Light" both in the sense of the Bible and the history of the Western initiatic tradition where Light has generally referred to knowledge and understanding. So, this amounts to (if I can so boldly pare Pike down to modern lingo), "if Lucifer is the light bearer and we talk about Light all the time, WTF?!" and he continues...
and with its splendors intolerable blinds feeble sensual or selfish souls? Doubt it not!
Okay, so here's the punchline. You have this idea that knowledge and understanding come with this spirit of darkness. Is that true? Of course it is! Look at any aspect of life from physics to personal relationships. The more you truly understand, the more you are entrusted with potentially harmful capabilities. Physics can give you the key to solving the world's energy problems or building a bomb of horrific potential. Understanding personal relationships can lead you to helping others or to Red Pill-style manipulation of them.
So my own interpretation, here, is:
The Mason is engaged in a quest for knowledge and understanding, but beware: what you bring to that process is your moral compass, and those who fail to apply that compass and seek "feeble, sensual or selfish" ends will undo all of the work that they have done to get there and end up with nothing (being "blind" to the Light).
Doubt it not, indeed.