Sentence:  In your zeal you may not feel you are undertaking a thing for your own sake but think you are doing so for God. Nevertheless, you should remember that at the time of great excitement as though you were on <WSD>cloud nine</WSD>, you may perhaps be most fleshly! 
Meaning of the word marked with <WSD> tags:  "Often in the phrase" '''(on cloud nine)''': a state of bliss, elation or happiness.