Albert Barnes on Revelation 17:7

And the angel said unto me, Wherefore didst thou marvel? He was doubtless struck with the appearance of John as he stood fixed in astonishment. The question asked him why he wondered, was designed to show him that the cause of his surprise would be removed or lessened, for that he would proceed so to explain this that he might have a correct view of its design.

I will tell thee the mystery of the woman. On the word mystery, Rev 17:5. The sense is, "I will explain what is meant by the symbol--the hidden meaning that is couched under it." That is, he would so far explain it that a just view might be obtained of its signification. The explanation follows, Rev 17:8-18.

And of the beast that carrieth her, etc. Rev 17:3.

(c) "woman" Rev 17:1 (d) "beast" Rev 17:3