Commentary for Deuteronomy 29:15

כי אתם ידעתם וגו׳ FOR YE KNOW [HOW WE HAVE ABODE IN THE LAND OF EGYPT] etc. — The meaning of these verses is: Because you have seen the conduct of the other nations, and perhaps the heart of one of you might beguile him to follow them, — as it goes on to state, “Lest there should be among you a man, or a woman … [whose heart turneth away this day from the Lord]”, — on this account I must place you under an oath.

FOR YE KNOW HOW WE DWELT IN THE LAND OF EGYPT etc. AND YE HAVE SEEN THEIR ABOMINATIONS. Because you have seen the nations that worship idols, and perhaps the heart of one of you might beguile him to follow them.

כי אתם ידעתם את אשר ישבנו, and this is why you have to be concerned that there should not be among you איש או אשה, neither a man nor a woman who would seduce you to follow the vain pursuits of the nations with whom you will be living in close proximity, and who might be the cause that you would default on the undertakings in this covenant. This is the reason I have insisted that all of you be present at this ceremony, seeing that G’d examines hearts He will know who only pays lip service to this covenant and who is sincere about it. You will not be able to deceive Him.