Be ready, because the Son of Man will come at an hour when you do not expect him.

When Jesus warned us to be ready for His second coming at the end of the age (Matthew 24:44), He knew that many Christians with weak faith would break under the pressure of persecution (Matthew 24:9) during the great tribulation (Matthew 24:15-25) and worship the beast to save their earthly lives (Revelation 13:14-15). Sadly, in doing so these rebels (2 Thessalonians 2:3) will lose their eternal lives (Mark 8:34-38) and be left behind when the angels come to gather the elect (Matthew 24:37-41).  to face God’s wrath and eternal punishment in the Lake of Fire (Revelation 14:9-11). 

Then they will persecute their former Christian family members and friends (Matthew 24:10). Sadly, in doing so these rebels (2 Thessalonians 2:3) will lose their eternal lives (Mark 8:34-38) and be left behind (Matthew 24:37-41) to face God’s wrath and eternal punishment in the Lake of Fire (Revelation 14:9-11). 

Jesus certainly had good reason to tell us, "be ready"! 

So, can church-going Christians not go to heaven? Yes! People aren't saved through church membership, they are saved by being in a right and real relationship with God through faith in Jesus Christ. They believe in Jesus (John 3:16) from the heart (Romans 10:9), they openly declare Jesus is Lord (Romans 10:10), they have repented of their sins and are baptized (Acts 2:38); and they love Jesus enough to obey His commands (John 14:21-23). 

when you're in a right relationship with God, you can loose your salvation (Matthew 

 While it cannot be taken from them, some Absolutely! Of course the first question is did they ever really have it. Jesus wrote a letter (Revelation 2:1-7) to the once thriving church in Ephesus (Ephesians 1:15-16) warning them to turn away from religiosity and return to Him, their first love. And if they didn't, Jesus said they would lose their place in heaven . In another place, Jesus painted a word picture of Judgement Day where Christians "in name only" were denied access to heaven because they weren't in a right relationship with Jesus (Matthew 7:21-23). So, yes! It can and will happen.  

Jesus said this in Matthew 7:21-23, “Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but only the one who does the will of my Father who is in heaven. Many will say to me on that day, ‘Lord, Lord, did we not prophesy in your name and in your name drive out demons and in your name perform many miracles?’ Then I will tell them plainly, ‘I never knew you. Away from me, you evildoers." 

So, simply belonging to a Christian religion is no guarantee of salvation. Religion doesn't save, Jesus does! And we must stand firm in our faith to the end to be saved (Matthew 24:13)  

Therefore, heaven is only open to people who have a right relationship with Jesus—people who truly believe in Him (John 3:16) with their hearts (Romans 10:9) and are willing to say “Jesus is Lord” out loud (Romans 10:10). People who turn away from sin and are baptized (Acts 2:38), and who love Jesus enough to obey His commands (John 14:23-34) for all the right reasons (Proverbs 16:2). People who are willing to give up their life to save it, and save their life by giving it up. And if you want to reach this level of faith, hope, and love in Jesus so you can stay strong till the end and be saved (Matthew 24:13), the time to get ready is now.

Don't wait until it's too late!