Well the original wording is ekklesia. This has been translated to church since approx King James version. Church then is a typical Christian gathering, But ekklesia actually means a congregation of people, and can apply to a congregation in a synagogue just as well
G1577 - ἐκκλησία ekklēsía, ek-klay-see'-ah; from a compound of and a derivative of ; a calling out, i.e. (concretely) a popular meeting, especially a religious congregation (Jewish synagogue, or Christian community of members on earth or saints in heaven or both):—assembly, church.
www.blueletterbible.org
Also, as Israel ceased to exist after around 70AD for most of the last 2000 years Christians have thought that any mention of Israel in NT prophecy could only be symbolic of the christian church, not actual Israel. Israel exists again of course, the prophecy of Ezekiel, the dry bones being given flesh and coming to life again, thats Israel. Anyway, point is Israel exists again so much of the prophecy about Israel is, well, about Israel & the Jews. Most of the Bible, including from book of Hebrews on in NT (its literally called Hebrews), is Jewish scripture.
As to the 7 churches being 7 Jewish congregations, please watch this:
Basically, the church (the body of Christ) is raptured out at the start of the tribulation. God then ends the age of the Dispensation of Grace during which He saved the Gentiles (any Jews too if they believed in Christ), and thereafter reinstates the
Law of Moses & turns His attention back to Israel & the Jews (the bride of Christ) to fulfill all His promises made
under the Abrahamic covenant He has with the Jews. He then takes the Jews through the 7 year tribulation to judge, purify & save them, at least those that turn to Him (2/3 wont).
At the end of 7 years He establishes the Millennial Kingdom, a Jewish Kingdom as He is the
Jewish Messiah & Jewish High Priest, for 1000 years. After the Rapture the church is not on earth anymore so the book of Revelation is not about the church. Israel will be the dominant nation of the world for 1000 years.
24 elders are the 12 apostles + 12 Jewish patriarchs (1 from each tribe), literally 24 people.