We all are going through trials at certain points of our life when Satan makes requests of God to swift us and sadly many fall and do not stand up. Is it because they are lukewarm Christians or lacking of faith?
Dont let the normal few make you feel unwelcomed. Some doctrines like the trinity or Jesus as the Messiah should be heavily defended but others like the doctrines I mention below only separate the churches.
Just in case you dont pick up on the 2 doctrines that will come into debate over this question. One believes that a Christian once saved cannot lose faith and lose salvation while the other belief talks about the dangers of falling away or being led away by false teachers can in fact if the individual who once believed later in life loses their faith and denies the Savior then the individual could lose their salvation.
Either way this has been debated by scholars for centuries and probably will be until Christ returns. Really not important other than we do see Christians who walk away from the faith due to hardships or cultural pressures.
The only thing we know exactly is no matter if they are still saved or not, their destination is going to be filled with pain from living a rebellious lifestyle and should help and pray for them.
The topic of Hell will also bring you different doctrines. Some believe no one is currently in Hell and everyone dead is in a soul sleep. This lines us with the 7th day Adventists. Awaiting for judgment day.
Some believe Hell is eternal.
Some believe Hell is experienced after death and in Revelations the second death destroys Hell and all the souls within it. They say this is God's final offer of mercy and not eternal punishment.
Either way the topic of Hell has also been debated for centuries. Still the only thing that matters is that Hell exists and you only have in life the opportunity to accept the grace of God.
Also your question kinda sounds like the thoughts are coming from the interaction between the Devil and God at the beginning of the poem Job. Some believe that because Job is written like a Hebrew poem that the interaction was not the normal interaction between God and Satan but more of a touch of literary imagery.
Some believe regardless of poetry it means exactly what it says.
But anyways we do not see the heart of others or know their future like God. They may return or maybe not. Many reasons for why people lose faith. A lukewarm believer in scripture has a very stern warning and shouldnt take for granted God's patience with rebellion. The usual reasons are because of selfish fleshy desires like sex, money, or power. Others it is emotional as in they was hurt in some way by a church, individual, or thoughts that God didn't heal their child etc. A small percent is intellectual as in they dont see the evidence.
Often times the selfish desires will hide behind the emotional or intellectual reasons. As with these they truly do not care if God exists or if Christianity is true. No amount of evidence could convince them.
Hope this helps. May be confusing because of people cherry picking doctrines without explaining the roots of their beliefs. I wish we could be one congregation or one sect of Christianity but unfortunately we disagree on certain doctrines. Thankfully most congregations are united on the core doctrines and for the most part work towards the greater good.