There are two main problems with believers in the visible church today, and unfortunately, they both center on the most important possible subjects for humans: salvation and sanctification.
One doctrinal problem is that church members or professing Christians have wrong ideas about what it takes to be saved. They say, or their preachers and teachers and denominations say, that it takes repentance from sins, belief in Jesus, “commitment” to discipleship, and lifelong perseverance to be saved.
Biblically, this is not true. Biblically, to be saved, it takes only a moment of faith in Jesus to be saved forever. It does NOT take repentance from sins or a commitment to a lifetime of discipleship, and it does NOT take perseverance in a lifetime of discipleship.
Secondarily, there is false doctrine in the visible churches regarding sanctification. Sanctification (holiness and righteousness) is not something that someone strives after in his or her flesh (their natural abilities) to achieve.
Sanctification is something that is given to you, whole and perfect and entire, in Christ, at the moment you believe in Him.
Now, this does ~not~ mean that in practical living terms a person is perfect from the moment of belief.
But it does mean, in spiritual terms, that a person is perfect in the sight of God. So a person’s sanctification is not something he strives for but something rather he believes in and lives from.
So, regarding salvation, a person rests in the fact that he is saved, and not that is he trying to be saved.
And, regarding sanctification, a person lives from their perfect sanctification and holiness and righteousness in Christ, not that he is striving to attain these goodnesses.
We should not, and actually cannot, strive to attain what God has freely given us.
The New Testament says to “work out your salvation” –but the salvation must be there ~first~ to be worked out.
And the only way a person can have peace and rest in working that out is to know that they are saved already, and to know also that they are sanctified already, NOT that they are doing things to be saved and doing things to be sanctified, but that this is their condition already, in Christ.