Why Church?

I. God's People, Christ's Priority

God has a people (Ex 6:6–9, 1 Pet 2:9–12).

God's community begins and ends in love that begins in God (Deut 7:7–8, Hos 2:19–20, Eph 5:25–27).

The Father's love sent Jesus his only Son into the world to seek and save his 'lost sheep' (Matt 15:24)

and make them "the light of the world" (Matt 5:14–16).
Building a community of disciples was and is Jesus' top mission priority.
(We build on the rock of his Word, but Jesus builds too: he builds us upon it: 1 Cor 3:9.)

This turns out to challenge our cultural (and even Christian cultural) habits, shaped by influential cultural forces:

Secular historicists and social scientists see only overlapping, shifting, competing, often compromised 'Christian traditions.'
Modern individualists push back that churches are mere political structures, 'organized religion.'
Social engineers see vehicles of social power to encourage, coopt, or weaken.
Consumerists treat churches similarly, as dispensable means of personal advantage or encumbrance.

(None of that invalidates God's work creating a people for his own possession and purpose.)

II. Reassembling "The Israel of God"
ekklêsia means assembly, gathering, reunion.

God assembles "his people" Israel (Ex 3:7, Deut 4:10 LXX) and assembles all his nations through Israel (Gen 12:1–3, Ps 2:6–8).

Israel assembles officially as qihal / ekklêsia (1 Kings 8:14; Deut–2 Kings, 1–2 Chron, many Psalms, minor prophets LXX), whether or not they are worthy.

Later, God scatters apostate Israel among the nations (2 Kings 25).
God regathers Israel out of love (Hos 11:1–4, Jer 31:1–4), prophesying and beginning its return in the OT

(Jer 3:14–17, 2 Chron 36:22–23, 1 Pet 1:1, Eph 1:22–23).

The church is vitally related to ethnic Israel and its mission (Rom 9–11 interpreting Deut 32 and Isaiah; Matt 1:1–17, 10:1–23),

but through Abrahamic faith, not flesh (Rom 4, interpreting Gen 15),
in Christ's fulfilling and redefining love (John 13:34–35).

III. Why an Ekklêsia is Bigger than Just a Synagogue
It's easy to retroject our contemporary forms of 'church' into biblical settings, but it's not clear that we should:

Jews in the NT already had get-togethers called synagogues,

ruled by one or more rabbis (basically a pastor-teacher; see Luke 8:49, 13:14, Acts 13:15) and elders,
with much more participation and dialogue than traditional churches today (Luke 4:16–30, 4:44, 6:6–11, 13:10–21, John 18:20, Acts 9:20, 13:14–47, 17:1–5, 10–12, 16–17, 18:4–11 etc.).

Why didn't Jesus-followers use the same term? (In much of the LXX it translates qihal; see below.)

And why don't we see pastor-led congregations in the NT?

Christ gifts the church with roles for fulfilling his Great Commission to regather, multiply, and mature God's People ('APEST': apostles, prophets, evangelists, shepherds, teachers; Eph 4:11–16)

in different expressions: PST in congregational life (modality, 'settlers'), AE in outreach (sodality, 'pioneers').

IV. Unpacking Ekklêsia's Resonances
Ekklêsia respects the church's present missional context between Christ's ascension and return,

as the unfolding means and fruit of fulfilling God's call to OT patriarchs and prophets.

Ekklêsia respects that the Kingdom is "already" (Matt 12:28) and "not yet" (Matt 13:47-50),

so the church "manifests the Kingdom without being identified with it."

Ekklêsia emphasizes the church's concreteness (so Acts 2's church circle).
Ekklêsia recognizes that the church is personal, a 'who' (networks of loving disciples) more than a 'what' (institutions, buildings, labels).
Ekklêsia respects its center, not just its boundaries

(whether in Catholic, Protestant, or Pentecostal fashion).

Ekklêsia suggests what the Nicene Creed lists as theological 'marks':

unity (manifesting God's), holiness (made for special use), catholicity (being whole), and apostolicity (being grounded and sent).

V. What About the 'Old' Israel?

This begs the question of how the church built upon Jesus relates to that people Moses is addressing—biological Israel.
What is "the Israel of God"? (Gal 6:16).

Supersessionism: The Church replaces Israel as "the new Israel" (classical theology).
Dispensationalism: The Church and Israel live under two different and still active covenants.
Pluralism: The Church and Israel have different ways to salvation (some varieties of Dispensationalism).

Paul's more complicated vision (Rom 9–11, interpreting Deut 32): All along God chose (elected) some to gather from among all nations (Isa 11:10 in Rom 15:7–12). Someday "all Israel will be saved" by faith (Isa 59:19–20 in Rom 11:26–27, concluding his thesis announced in Rom 1:16–17).