G'day Alex, I agree with your comment that it is a good video with much to be agreed with. Yet it is necessary to correct what might just be a misunderstanding on your part, above quoted, on account of wresting with a short video on a difficult topic.
To be sure, Ron Cantor says, at the 4:50-53 mark per your time reference.
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As you can see, Cantor does not use the term "Ekklesia", nor has he inserted "Ekklesia" into the graphic, as your comment indicates.
What Cantor is saying is just what he has said in the introduction to his video at 0:23 mark (next pic): "Kyriakon" is not used on the Greek NT for the body of believers, i.e. the people.
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Furthermore, elsewhere Cantor says that the Greek word "Kyriakon", as primarily used in reference to a religious building in classical Greek usage, was employed to underpin the term "Church" (via the common use of "kirk" at that time) according to King James' insistence, rather than "Ekklesia", which is used in reference to a gathering of people.
That is, as reading elsewhere will show, King James translation is anchored to the local use of 'Kirk', as was used for the cathedral and parish buildings 'dedicated to the Lord', rather than going back to Ekklesia with its foundational etymology of referring to "the called-out ones". Consequently, the translations we have these days that do not use the likes of Congregation and Assembly, clearly people-oriented terms, allow for and even invite by default the continuing misunderstanding that the Church is much ado about buildings (built places) and the activities centred on those places.
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Ron Cantor has attempted to outline, essentially, that when we read (the poorly chosen term) "Church" in the NT our understanding must not be about buildings (Kyriakon) as is so commonly understood. Rather, "Church" is to be about the people-gathered, because of the original God-inspired word, "ekklesia". That is a difficult task to do so in such a brief video.
I did appreciate how Cantor demonstrated that the use of ekklesia is not limited to just a gathering of believers but of any gathering of people who have been 'called out' for a purpose. Theologically, IMHO, Luke's use of ekklesia to refer to opposing groups is to accent and contrast the opposing world-views of people and the one/s they are following. Do they follow Jesus who has called them out to himself and his will, or do they follow the powerful people and politics of the day?
Nonetheless, it is not easy to follow Cantor's challenging argument with ease. Mental gymnastics (not contortions, by any means) and pre-awareness of the factors, concepts, etymologies, historical uses and biases concerning ekklesia, kyriakon, kirk, church, etc, are not easily held or apprehended -- but helpful in viewing this video. In my view Cantor could have done well to take more time and included more graphics. Overall, I think Cantor's presentation is correct, albeit a bit attenuated. More study is needed by us all on this topic.
Alex, I appreciate you bringing this to my attention -- with thanks. Please help me out by identifying any problems in what I have written, including typos. Happy to hear from you and others on "ekklesia".
Peter Johnson, Newcastle, Australia.