So you would see any Church not teaching a clavinistic view on scripture as not being a Bible based church, not offering the real Gospel to its members then?
There is only one Gospel (Gal 1:6-12; 2Cor 11:1-4; Jude 1:3). C.H. Spurgeon who is certainly not infallible believed and preached that what is known as Calvinism IS the Gospel. And there are myriad others both before and after him who have believed the same thing. The universal Reformed churches in 1619 at the Synod of Dordt concluded that Arminianism was a damnable heresy. What is believed in the majority of churches is even worse; semi-Pelagianism, Pelagianism, Liberalism, etc. So, pray tell, how can someone believe upon the Christ of the Scriptures from hearing a false Gospel under a false teacher? The biblical gospel emphasizes the total depravity and inability of man, that all men by nature are under the wrath and judgment of God, that God is infinitely holy and is at enmity with man, that Christ who is God in the flesh lived a perfect life, was crucified, died, buried and rose from the dead in order to save a particular people from their sins, having taken upon Himself their sins, that the Spirit of God gives life to spiritually dead sinners creating in them a heart of flesh, a renewed nature, that those who are born anew are first deeply convicted of their sin and sinfulness, under God's wrath and just judgment, are guilty before God and have never done a single good thing in their life, that Christ's perfect righteousness must be imputed to their account in order for the remission of their sins and be reconciled to God... etc. See my article: A Gospel Summary
. Another article I would recommend is: Is Calvinism the Gospel?
. Yes, it is possible that someone who attends or is a member of a false church to come to a saving faith of Christ. But NOT because of what they hear in that church but through either their own reading of the Bible and/or through the witness of a true child of God who brings the true Gospel to them.
Under the typical preaching/teaching of the modern church most are under the false assurance they are saved because they "asked Jesus into their heart", read a sinner's prayer, etc., etc. ad nauseam which is classically known as Sandemanianism
, aka: Easy Believism.
A sinner is not saved because
they believe Calvinism!! But right doctrine will be believed by a sinner saved by the work of the Spirit who enlightens the mind to the things of God which were before foolishness to him. And, it is also not true that only those who are fully knowledgeable of doctrine can be saved. Through the process of sanctification the Spirit brings God's adopted children to a greater knowledge of the truth as He wills for each of them.