While there are certainly unbelieving members of churches, having no faith in the Lord for saving forgiveness and cleansing, the Scritures record honest believers, that do forsake the Lord by transgression, beginning with Adam the son of God. The anointed King Saul. And of course the chosen apostle Judas Iscariot.committed by professing members of the visible church who were never true believers to begin with.
And that includes all the believing Jews, that forsook the Lord at the cross, and were all cut off from the Israel of God as unbelievers.
And so, the warning of Heb 10 and Rom 11 is the same for Paul and us all, that we should not be highminded in our faith, and presume our own justification and guiltlessness by faith, while likewise transgressing after the manner of Adam.
Rom 11:18
Thou wilt say then, The branches were broken off, that I might be graffed in. Well; because of unbelief they were broken off, and thou standest by faith. Be not highminded, but fear: For if God spared not the natural branches, take heed lest he also spare not thee. And they also, if they abide not still in unbelief, shall be graffed in: for God is able to graff them in again.
We see once again, how that the disobedient Jews were counted as unbelievers by forsaking Jesus, but are grafted in again by repentance and faith toward Jesus for saving mercy and grace. So also we are warned, that we too can be cut off by transgression against Jesus, but can also repent likewise and be grafted in again.
However, if we become presumtpive in our own transgression by highmindedness in our own faith, then we will not humble ourselves with the guilty called to repentance. Rather in our own decpetive faith and doctrine, we can remain condemned with the unrepentant transgressors of the world.
1Jo 5:16
If any man see his brother sin a sin which is not unto death, he shall ask, and he shall give him life for them that sin not unto death. There is a sinning unto death: I do not say that he shall pray for it.
If we are transgressing and seeking saving mercy and foriveness from Jesus Christ, we can pray for ourselves and others likewise. But, if we are unrepentant without godly sorrow, then we will not pray to God, nor are we to pray for others that likewise harden themselves and repent not.