Ecclesia just means assembly or congregation, all examples of church in the NT are little c-churches.
This is sheer nonsense (and an extraordinarily ignorant thing for any serious student of the Bible to assert):
Acts 20:28 (RSV) Take heed to yourselves and to all the flock, in which the Holy Spirit has made you overseers, to care for the church of God which he obtained with the blood of his own Son.
1 Corinthians 10:32 Give no offense to Jews or to Greeks or to the church of God,
1 Corinthians 11:22 . . . do you despise the church of God . . .?
1 Corinthians 12:28 And God has appointed in the church first apostles, second prophets, third teachers, then workers of miracles, then healers, helpers, administrators, speakers in various kinds of tongues.
1 Corinthians 15:9 For I am the least of the apostles, unfit to be called an apostle, because I persecuted the church of God.
Galatians 1:13 For you have heard of my former life in Judaism, how I persecuted the church of God violently and tried to destroy it;
Ephesians 1:22 and he has put all things under his feet and has made him the head over all things for the church,
Ephesians 3:10, 21 that through the church the manifold wisdom of God might now be made known to the principalities and powers in the heavenly places. . . .  to him be glory in the church and in Christ Jesus to all generations, for ever and ever. Amen.
Ephesians 5:23-25, 27, 29, 32 For the husband is the head of the wife as Christ is the head of the church, his body, and is himself its Savior.  As the church is subject to Christ, so let wives also be subject in everything to their husbands.  Husbands, love your wives, as Christ loved the church and gave himself up for her, . . .  that he might present the church to himself in splendor, without spot or wrinkle or any such thing, that she might be holy and without blemish. . . .  For no man ever hates his own flesh, but nourishes and cherishes it, as Christ does the church, . . .  This mystery is a profound one, and I am saying that it refers to Christ and the church;
Philippians 3:6 as to zeal a persecutor of the church, as to righteousness under the law blameless.
1 Timothy 3:15 if I am delayed, you may know how one ought to behave in the household of God, which is the church of the living God, the pillar and bulwark of the truth.
The Holy Scripture says we are one “body” in Christ, it doesn’t say we are one church in Christ.
This is nonsense as well, because St. Paul writes:
Colossians 1:18, 24 He is the head of the body, the church; he is the beginning, the first-born from the dead, that in everything he might be pre-eminent. . . .  Now I rejoice in my sufferings for your sake, and in my flesh I complete what is lacking in Christ’s afflictions for the sake of his body, that is, the church,
In other words, the Body of Christ = “the Church.” Therefore, if there is “one body in Christ” (Rom 12:5) and this “body” is “the Church” (Col 1:18, 24), then there is one Church in Christ also, by simple logic (a = b, therefore if a = c, b also = c). The Church is also called the “body of Christ” (1 Cor 12:27; Eph 4:12).
The Bible states that Paul persecuted the Church, and Jesus Himself equates that with persecuting Himself (since the Church is the Body of Christ):
Acts 9:4-5 And he fell to the ground and heard a voice saying to him, “Saul, Saul, why do you persecute me?”  And he said, “Who are you, Lord?” And he said, “I am Jesus, whom you are persecuting;
Jesus also referred to “my Church” when He commissioned Peter to be the leader of it (the first pope):
Matthew 16:18 And I tell you, you are Peter, and on this rock I will build my church, and the powers of death shall not prevail against it.
The Roman Catholics high jacked [sic] the term Ecclesia to refer to an organisation rather than to people (Protestants have kept the same terminology usage because it is now part of the vernacular but it’s not biblical in its meaning)
The claim that Catholics have perverted the biblical meaning of “church” is the exact opposite of the truth. It’s Protestants and your own Adventists who have done so. But many Protestants still refer to “the Church” because it is an undeniable NT concept. They just deny that it is institutional, historical, founded on apostolic and papal succession, centered in Rome, and infallible and indefectible, as the Bible teaches.
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Summary: Seventh-Day Adventist disputes the use of “the Church” in the New Testament, referring to an institutional organization, founded by Jesus Christ upon Peter.