Hebrews 3:12-14 (NKJV)

12 Beware, brethren, lest there be in any of you an evil heart of unbelief in departing from the living God; 13 but exhort one another daily, while it is called “Today,” lest any of you be hardened through the deceitfulness of sin. 14 For we have become partakers of Christ if we hold the beginning of our confidence steadfast to the end,

This verse is commonly used to illustrate that people can ‘depart’ from the faith if they harbor unbelief in their hearts. The conditional word “if” is used to hit home the idea that true Christians can lose salvation.

Explanation

This passage was intended as a warning for those  who were ‘impressed’ with the teachings about Jesus as the Messiah and the new covenant He established. However, they were constantly tempted to return to their “ineffective Levitical system (the old covenant).

The people addressed in the book of Hebrews deceived themselves by reasoning that their rejection of Jesus Christ was only because they remained loyal to the old system. But in reality, their loyalty to the Leviticus system was a rejection of the living Word (Heb. 4:12) of the living God (Heb. 3:12), who had made a new way possible through Christ (Heb. 10:20).

In continuing with the path of unbelief towards Christ’s forgiveness, people risk being excluded from God’s eternal rest.

As for the phrase “departing from the living God,” does not necessarily mean they were once part of God but are now not, rather it means that they stood apart from Him, never having belonged to Him.

We read in first Timothy that in later times some will fall away (aphistemi) from the faith, listening to deceitful spirits and doctrines of demons (1 Timothy 4:1).

Luke uses the same root word aphistemi to explain Jesus’ explanation of the seed that falls on stony ground. “And those on the rocky soil are those who, when they hear, receive the word with joy; and these have no firm root; they believe for a while, and in time of temptation fall away (aphistemi).” (Luke 8:13)

Their fallaway is caused by the failure of the seed of the Word of God to take root. Aphistemi does not indicate an uprooting, as there was never a root, and therefore this person was not a believer.

Aphistemi does not mean that at one time they belonged to God and now they no longer belong to Him, but rather that they stood away from God, never having belonged to Him.

Therefore, we can conclude from this verse that hardened hearts only reveal outwardly that a person is not a genuine Christ-follower (and has never been one).

Authentic believers do not harden; rather, they persevere, holding fast to their original confidence.

It is clear from this verse that anyone who claims to be saved must examine themselves carefully and make sure their faith is genuine. A person who lacks perseverance in faith and obedience has a real reason to doubt whether they have ever been saved.