Sentence:  ... I ſhall now proceed to consider what the "Ancients" taught concerning the "Deſcent", or <WSD>"Illapſe</WSD>" of the "Holy Spirit" upon the "Symbols", or upon the "Communicants" in this Holy Solemnity. ... Why ſhould the <WSD>"Illapſe</WSD>" of the Holy Spirit be ſuppoſed to work any greater, or any other "Change" in the "Elements" of the "Euchariſt", than in the "Waters" of "Baptiſm"? 
Meaning of the word marked with <WSD> tags:  A gliding in; an immission or entrance of one thing into another.