"Take care, brethren, that there not be in any one of you an evil, unbelieving heart that falls away from the living God." -Hebrews 3:12
The writer of Hebrews is writing to the "brethren" which would indicate he is writing to believers who are part of the church, encouraging them to be steadfast, and not to fall away from the Lord through a lack of belief. Pretty simple and straight-forward.
1 Timothy 4:1 "But the Spirit explicitly says that in later times some will fall away from the faith, paying attention to deceitful spirits and doctrines of demons"
We learn in 1st Timothy that Holy Spirit warns believers that in the last days some will "fall way" from the faith. To fall away from the faith, one must already be part of the faith. They will be led astray and deceived by demons and evil spirits. They lose their salvation through being deceived.
2 Peter 3:17 "You therefore, beloved, knowing this beforehand, be on your guard so that you are not carried away by the error of unprincipled men and fall from your own steadfastness"
In 2nd Peter we learn that the "beloved" which would point to believers, must be on their guard so they are not carried away by the errors of those who do wrong, and fall from their steadfastness. Falling away can happen due to the poor example of others.
1 Corinthians 9:27 ESV "But I discipline my body and keep it under control, lest after preaching to others I myself should be disqualified."
A pastor preaching the gospel must be careful to discipline his or her body and live out holiness, or they may end up disqualifying themselves from salvation. They could end up falling away if they aren't careful to discipline their bodies.
1 Corinthians 10:12 ESV "Therefore let anyone who thinks that he stands take heed lest he fall."
A simple reminder in 1st Corinthians tells us that we must be careful when we stand, to make sure we don't fall.
Revelation 2:4-5 ESV "But I have this against you, that you have abandoned the love you had at first. Remember therefore from where you have fallen; repent, and do the works you did at first. If not, I will come to you and remove your lampstand from its place, unless you repent."
Jesus speaks to the seven churches in the book of Revelation, and he calls the church, which references believers, to repent because they've fallen away. And Jesus says if you don't, I'll remove your lampstand. So once again, we see that believers can fall away. Even whole churches can fall away. But they can also repent and turn again to the Lord.
Hebrews 2:1-3 ESV "Therefore we must pay much closer attention to what we have heard, lest we drift away from it. For since the message declared by angels proved to be reliable, and every transgression or disobedience received a just retribution, how shall we escape if we neglect such a great salvation?"
Here we see the idea of "drifting away." Often we see people attending church faithfully, loving Jesus, praying and reading their Bible. But they slowly begin to fall away and pretty soon we see them at church less and less. And eventually they are gone all together. They drifted away from the truth, and back into the world.
Finally, we see the parable of the vine and the branches. This is the clearest evidence of the possibility of falling away, if we disregard the important command of "abiding" or "remaining" in Christ.
“I am the true vine, and my Father is the gardener. 2 He cuts off every branch in me that bears no fruit, while every branch that does bear fruit he prunes[a] so that it will be even more fruitful. 3 You are already clean because of the word I have spoken to you. 4 Remain in me, as I also remain in you. No branch can bear fruit by itself; it must remain in the vine. Neither can you bear fruit unless you remain in me.
5 “I am the vine; you are the branches. If you remain in me and I in you, you will bear much fruit; apart from me you can do nothing. 6 If you do not remain in me, you are like a branch that is thrown away and withers; such branches are picked up, thrown into the fire and burned. 7 If you remain in me and my words remain in you, ask whatever you wish, and it will be done for you. 8 This is to my Father’s glory, that you bear much fruit, showing yourselves to be my disciples.
9 “As the Father has loved me, so have I loved you. Now remain in my love. 10 If you keep my commands, you will remain in my love, just as I have kept my Father’s commands and remain in his love. 11 I have told you this so that my joy may be in you and that your joy may be complete. 12 My command is this: Love each other as I have loved you. 13 Greater love has no one than this: to lay down one’s life for one’s friends. 14 You are my friends if you do what I command. 15 I no longer call you servants, because a servant does not know his master’s business. Instead, I have called you friends, for everything that I learned from my Father I have made known to you. 16 You did not choose me, but I chose you and appointed you so that you might go and bear fruit—fruit that will last—and so that whatever you ask in my name the Father will give you. 17 This is my command: Love each other. -John 15:1-17
Examine these additional scripture about falling away. Click here.